I decided to use ESXi4.0 for a Small Business server virtualization project. Everything seems to be working well with the exception of the USB devices. I physically connect a USB drive to the Host's USB port but I don't get it on the Guest. I tried a number of things like rebooting the guest OS, removing the USB and reconnecting it, nothing. Only thing I did not do is restart the host with the USB drive physically attached, but I should not have to do that with USB. Any thoughts? Thank you.
USB Support is not yet working.
You can virtualize the USB controller, but not the devices... so it isn't useful.
To use USB device into a VM you need VMware Server or VMware Workstation.
You cannot use ESX or ESXi. Maybe the future releases of vSphere...
If you need external storage support have a look at NFS. You can use very inexpensive desktop NAS devices (as long as they support NFS). Many of them support hot plug USB. You can also use NAS devices directly within the guest.