I have been using Parallels for some time, and have VMs with both Windows Xp and Linux. Today I configured "fast user switching" on my Mac Pro, logged in another user, started the OSXvnc server on it, and switched back to my login. The other user connected via ssh and vnc to his login, and we could both work. This worked fine until I opened a Linux VM. DISASTER! While nothing crashed, the mouse and keyboard would be unresponsive for 10-20 sec, I could move the mouse a few inches, and then wait 10-20 sec. This made the system completely unusable. As it happened, the other user was connected but idle at this time. Eventually I was able to release the focus from the parallels VM, and mouse and keyboard work fine in Mac windows. I switched to the other user and logged him out, came back to my login, and the Linux VM now operates normally. The other user did change his screen size to 1024x768 (mine is 1680x1050) -- we each saw our selected screen size, including switching to his login with the big monitor. I did not try a Windows VM with two users logged in.
