Problem we had with VMware and our iMac, when we plugged the mouse in via a HUB...
Plug the mouse in directly into one port and every thing else on the hub.
Its what fixed it for us.
Keyboard doesn't need it and really the memory sticks don't really either.
I just think OSX plays games with USB ports from time to time if they have multiple devices on one USB port via a USB HUB.
Also, we purchase a REALLY nice HUB (a Belkin powered hub) which helped a bit before we switched the way we are now.
Only the mouse seems to have issues that way.
Edit:
Our mouse is a Logitech something or other wireless one.