I ended up having to disable all audio in my Win7 guest - playing of any audio sound in it would cause the guest to freeze for a while - very annoying...
Since I still need audio for notifications etc, even if I give up on using lync for calls, I created a new windows 8 guest, and tried using that.
At least normal audio works fine in that, but when I try to use the usb headset with lync, lync freezes when trying to test the ringer, or after exiting the setting dialog if I don't test it. I can only unfreeze it by disconnecting the headset device in the VM devices menu, so it's totally useless.
Any chance someone from VMWare can tell us if this should work, and if so, if they're actually looking these problems we're all having?