While debugging winlogon.exe in a virtual Windows, I encountered a nasty VMware bug: Single stepping SYSENTER in the virtual OS will hard reset the host OS (not even bluescreen)!

Encountered with VMware 4.0.0.4460.

I determined that this bug is fully reproducable. My setup is: Windows 2000 Advanced Server hosting VMware, with a virtual Windows Server 2003, Standard Edition installation. Debug any program with WinDbg, breakpoint at ntdll!NtClose (or any other commonly used system entrypoint), and step through until you get to the SYSENTER instruction in the shared user/kernel memory map. Stepping through SYSENTER will cause the host machine to hard reset.

Actually i think that happened to me before, not to mention all the other hard restarts caused by... well... anything that just like an nt based system (based on my experiences anyways, bleck)