Seems pretty reliable here. I'm running RC2 build 1920 on a 2GB 2.66GHz Mac Pro. Stock Nvidia 7300GT video card.
I have VMs running Win98se and a couple of Linux distributions. I'm not exercising them very severely, though. I only use them for checking web browser compatibility, plus Windows for some specialised utilities, and Linux as a test web server and cross compilation platform.
The only issues I'm aware of are (1) copy/paste from OS X to Win98se only copies the first character of the clipboard, and (2) last time I tried build 1922 it kernel panicked and then disabled VT-X virtualisation, so I reverted to build 1920.