I've tried 3 different OS's with my current overclock, (see sig) Vista x64, WinXP x64 and Ubuntu 64bit. I had no issues or instabilities on any of them. I did have quite a bit of trouble installing XP x64 though, kept getting blue screens on install. I eventually got it stable by not using AHCI mode and using drivers from MSI's site not using ATI's drivers.

I'm dual booting with Vista x64 and Ubuntu, everything runs beautifully. I have not had one crash, blue screen, 100% stability. I probably have a really good X4 though, but I would have been more than happy with 3Ghz.

I don't know if some peoples problem is releated to the B2 stepping, immature BIOS etc. but I've been very very happy with my system. I would like to try running @stock frequency and lowering the CPU voltage, but BIOS 1.4 doesn't support lowering CPU voltage from stock for some reason.