A lot of people email and asking me about this question. Here is my compilation of the question and findings.
Q1. Is USB Support available in Hyper-V?
The answer is No!. No USB support natively built in into the Hyper-V.
How about Windows Server 2012? The answer is still NO! except for VDI over RDS. (refer to Scenario 2)
Q2. USB Support using Client Operating system?
Yes. Use Virtual PC for Windows 7. Please refer to http://www.microsoft.com/windows/virtual-pc/
More scenario, please refer to below
Scenario 1:- Any USB device to Guest VM
Use 3rd party tool which redirects any USB device (like USB dongles, USB modems, USB disks, etc.) over a local network from one server to another. One of the 3rd party tool is http://www.fabulatech.com/
Scenario 2:- USB to VDI. Guest VM is running Windows 7 or later
Use RemoteFX. It has functionality to redirect virtually any USB device transparently over RDP. Please refer to:-http://www.ms4u.info/2010/07/remotefx-usb-redirection.html
Scenario 3:-USB Thumbdrive to Guest VM for temporary copying data
1. Use Remote Desktop Connection. Before connect, change the setting on the Local Resources. Tick Ports, USB thumbdrive and other supported Plug and Play Devices.
After RDP. go to My Computer and you will be able to see the mapping to USB thumbdrive.
Hope this help to answer your doubt.