Accepted Solutions
...Data access: if every user has his own OS, then he has his own file system and data. No security issue...
I don't mean security of the guest OS. I mean security of the host computer if a "kid" needs to start up the computer and you're not home, but the keyboard and mouse config gets messed. The "kid" needs to access VMware Workstation to get to the USB menu, which means they now have access to the files on the host. Thus my example of password protecting the individual files/folders and not relying on the main logon account password.
...if I can't easily allocate hardware per virtual machine, than you are right, no point of going that way. and I was thinking of adding audio cards in order to provide audio.....
Audio can be done with USB sound cards. That then brings us to the question of enough USB ports, which may mean PCI USB card, and then do you have enough PCI slots. And my previous point that all of this extra hardware is adding up. You have to analyze if you're really saving that much $$$ by doing all-in-one versus individual low end machines. Imagine the "kid" playing a YouTube clip or some other Flash video that hogs the CPU, and bog down all the other users. (Or worse, WoW.) What did you really reduce other than the motherboard, case, power supply? The third user will need a video card since most cards can only handle 2 monitors. (Or fourth user, if you can also use built-in graphics.) But again do you have enough PCI slots for the USB cards you need to add? Or were you planning to get a ka-zillion USB hubs? That could restrict you on transfering large files to USB hard drives since you're sharing the USB bandwidth. (Oops, Bobby accidentally bumped the power cord on the hub, disconneting Becky's external drive while she was writing to the drive. Now the drive is corupt and she has to redo her homework. Daddy! And now Wifey says she can't open the tax files! :smileyshocked: )
...But what makes me worried is that you pointed that the VM world is not mature enough and not stable...
This "multi-user" thing was tried several years back without virtualization. You added a PCI card that gave you a monitor, keyboard, mouse connection. The cost was kinda high (~$300 per unit) and you still had to deal with things like limited hard drive space, (so add in the cost of additional hard drives,) buying additional sound cards, slowing down the host when one of the users inadvertently ran something CPU intensive, or locking up the system, forcing a reboot of everyone, etc, etc, etc. This was all without adding any of the limitations of virtualization so many of the issues I'm pointing out have nothing to do with the "maturity" of virtualization. It is limitations inherent with a shared PC project. My cousin was a librarian at an elementary school and was investigating such a system. Eventually, as PCs came down to under $1000, it was seen as more reasonable and easier to maintain (a.k.a. less specialized technical knowledge) to have "standard" PCs rather than "custom" systems, especially once it was factored in the much higher cost of the beefed-up host. And realize that this was a public elementary school, where the kids were going to do things that "broke" the system, both intentional and unintentional. Now place your stuff on the system and see how much your kids will crash your setup when they're Torrenting or YouTubing, despite your repeated warnings not to do so. (Because we know that kids always listen to their parents. 
)
So, if it's very small number of "trusted" users, that's fine. But the point is to go through all the theoretical senarios. So even if you didn't have to allocate hardware devices, then a multi-user system like this is still only for a very limited number of situations. As I said, theoretically possible. But practical only to a point.
Power/power down/rebooting - no issue. I have a Linux machine running for weeks. If host should be rebooted - let it reboot. Users can wait - they are not running ER. Again - better to reboot one host machine (e.g. due to system update, anti virus update etc), rather then reboot few machines due to same reasons. Also, host reboot can be planned to late night, lunch time etc.
I didn;t understand the problem with connecting external hardware: USB makes our lives so easy, USB3 may even bring graphic interface. Can;t I assign pre-determined host image to pre-determined set of kbd/mouse/monitor? or a "select image" window to allow the user select (with password) the needed image?
In both cases, yes, in theory. What I meant by not practical is that Murphy's Law often rears it ugly head and you get "unexpected" things like host lockups. And if the "guest" is your kid and you don't want them access to the host, you'll have to figure out how they're going to start the virtual machine without them logging on to the host. (e.g.: Power outage overnight. So have host autologon, but have all files and email clients password protected.)
As for USB, in theory you should be able to tell the VM which USB devices to autoconnect to which machine (It does in Fusion, but I've not done that in Workstation) but I've had some cases where it didn't remember so I had to go back and config stuff again. As in the previous example, you have to allow your "kid" to Workstation to config stuff if that happens.
All are YMMV type of stuff. So if it was a spouse or someone you trust, then that's fine. But if you try this for 1 spouse, 3 kids, 2 nephews, it'll probably be a full time job maintaining this. ("Dad! My Windows ain't working! Yeah, my mouse is on Becky's screen!...) Again, in theory, it's possible. But in a practical sense, Workstation wasn't designed with simultaneous multiple users in mind (other than remoting to the guest.) So beyond 1 or 2 guests, don't say we didn't warn you.
...Data access: if every user has his own OS, then he has his own file system and data. No security issue...
I don't mean security of the guest OS. I mean security of the host computer if a "kid" needs to start up the computer and you're not home, but the keyboard and mouse config gets messed. The "kid" needs to access VMware Workstation to get to the USB menu, which means they now have access to the files on the host. Thus my example of password protecting the individual files/folders and not relying on the main logon account password.
...if I can't easily allocate hardware per virtual machine, than you are right, no point of going that way. and I was thinking of adding audio cards in order to provide audio.....
Audio can be done with USB sound cards. That then brings us to the question of enough USB ports, which may mean PCI USB card, and then do you have enough PCI slots. And my previous point that all of this extra hardware is adding up. You have to analyze if you're really saving that much $$$ by doing all-in-one versus individual low end machines. Imagine the "kid" playing a YouTube clip or some other Flash video that hogs the CPU, and bog down all the other users. (Or worse, WoW.) What did you really reduce other than the motherboard, case, power supply? The third user will need a video card since most cards can only handle 2 monitors. (Or fourth user, if you can also use built-in graphics.) But again do you have enough PCI slots for the USB cards you need to add? Or were you planning to get a ka-zillion USB hubs? That could restrict you on transfering large files to USB hard drives since you're sharing the USB bandwidth. (Oops, Bobby accidentally bumped the power cord on the hub, disconneting Becky's external drive while she was writing to the drive. Now the drive is corupt and she has to redo her homework. Daddy! And now Wifey says she can't open the tax files! :smileyshocked: )
...But what makes me worried is that you pointed that the VM world is not mature enough and not stable...
This "multi-user" thing was tried several years back without virtualization. You added a PCI card that gave you a monitor, keyboard, mouse connection. The cost was kinda high (~$300 per unit) and you still had to deal with things like limited hard drive space, (so add in the cost of additional hard drives,) buying additional sound cards, slowing down the host when one of the users inadvertently ran something CPU intensive, or locking up the system, forcing a reboot of everyone, etc, etc, etc. This was all without adding any of the limitations of virtualization so many of the issues I'm pointing out have nothing to do with the "maturity" of virtualization. It is limitations inherent with a shared PC project. My cousin was a librarian at an elementary school and was investigating such a system. Eventually, as PCs came down to under $1000, it was seen as more reasonable and easier to maintain (a.k.a. less specialized technical knowledge) to have "standard" PCs rather than "custom" systems, especially once it was factored in the much higher cost of the beefed-up host. And realize that this was a public elementary school, where the kids were going to do things that "broke" the system, both intentional and unintentional. Now place your stuff on the system and see how much your kids will crash your setup when they're Torrenting or YouTubing, despite your repeated warnings not to do so. (Because we know that kids always listen to their parents. )
So, if it's very small number of "trusted" users, that's fine. But the point is to go through all the theoretical senarios. So even if you didn't have to allocate hardware devices, then a multi-user system like this is still only for a very limited number of situations. As I said, theoretically possible. But practical only to a point.