The PCIe multipliers come at some costs, besides money, like you cannot place devices that require a big number of lanes to funciton properly on a small PCIe. Like say 3 1x devices on a 1x slot. There is just no technical room for that.
On the other hand, GPUs do identify themselves as 2 devices, so from this point of view, we could assimilate PCIe multiplier to the same issues as GPU passthrough. So technically it should be possible, but practice will say which one indeed works fine and with what devices.
Regarding USB passthrough, I have no problems passing through any of my USB stuff: sticks, HDDs (both 3.5 powered or 2.5 non-powered), ps2 keybopard (with USB adapter) and USB mouse gone through a to_ps2 then to_usb adapters (I've got a KVM setup that uses ps2), a mustek video device used as a webcam, 2 USB hubs (1 not powered, 1 powered that also has audio and LAN going through and showing up as USB devices working fine), a video to USB device (as my GPU passthrough is not working; the new MB is scheduled to arrive from the US sometime in January),
I also connect to the USB my Canon IS3 for picture download, works fine as well.
Connecting my HTC tilt2 as storage works fine, for active sync something is not working right but I'm not sure if I actually installed all the needed stuff for it as I only use it as storage when connected.
I also got my lexmark printer connected through USB and working fine.
Yes, my main development machine is a VM on my ESXi 5.0, which is why I'm so USB driven 
I would suggest looking at drivers maybe? If your DiNovo works fine during bios setup, I don't see any reason for its basic keys to not work fine passed through USB as-is.
Have you got DXVA working?
This is a big one for me as with 1080p content trying to play it without it really is a no go
Think my bank account is about to be damaged by the looks of things though 
My 7750 works fine with DXVA, it is single slot, and 90 bucks after rebate right now - practically free
http://www.newegg.com/Product/Product.aspx?Item=N82E16814150612&Tpk=xfx%207750
I question for the guys running the Gigabyte GA990FXA-UD3 or Gigabyte GA990FXA-UD5 is the on board nic and any of the on board sata supported in Esxi 5.0 by default and if not did anyone manage to get drivers working? Also can you pass though the on board sata controllers on that board? I just want to run one SSD into esxi and i want to pass through the other controllers and drives if possible to get max speed in my NAS VM. Also is there more than 1 usb controller as i was hoping to run a media pc and a desktop pc as Vms so need 2 keyboards and 1 mouse. My media pc will be openElec hopefully and i have an infrared to usb converter that works so much better than normal IR for controlling media pcs.
Also someone mentioned you can pass through the graphics card running the VM console! just wondering if i stop the VM using that graphics card would it flip back to the console or not. Also has anyone ever found a way to pass through the hdmi from one graphics card to one VM and the vga and dvi to another? I know it is prob not possible but i am trying to get 3 displays over DVI for my desktop without a high power using card or a $300 card if i can help it. Lastly if you put a vm to sleep can you start up another VM while the other one is a sleep that uses the same cards that was passedthrough to the one i put to sleep? Wanted to have a few VM's for my desktop so i could switch between windows7, 8 and linux.
Also just wanted to say thanks for all the help so far! Been a long time since i came across such a great group of people helping everyone and even answering stupid questions without complaints
Also to the other person looking for a lot of PCIe slots have a look at the Gigabyte GA990FXA-UD5 that thing has 2x16, 1x8, 2x4, 1x1 and a pcie. THat is what i am looking at using.