|Windows 7 KVM guest with Spice USB Redirection on Fedora 16 host|
Fortunately, Spice's USB network redirection seems to work great. virt-manager is not capable of configuring or using it directly, but following these directions and using the spicy client, I managed to redirect USB 2.0 devices to my KVM guest. It even has an option to automatically redirect newly plugged devices, and it does so intelligently to the host or guest depending which window has keyboard focus at that moment.
spicy client seems better than spicec or virt-manager, although Shift-F11 to escape full screen mode seems to be broken. Until this bug is fixed, a temporary workaround is to CTRL-ALT-F2 and kill spicy in order to escape. UPDATE: It seems Shift-F11 fails to both enter and exit full screen mode. Full screen can only be entered from the View menu of spicy. However Shift-F12 to ungrab the mouse does successfully escape from full screen spicy.