Our application makes use of QueryPerformanceCounter to measure timings. When running it on Amazon EC2 instances we are noticing number that are out of whack. The symptoms look very similar to what has been reported with virtualized machines on HP proreliant servers, however all the articles state that this was not the case for Windows Server 2008.
The articles recommended modifing the boot.ini to /USEPMTIMER - however, this seem to be missing from the documentation on bcdedit - which replaced boot.ini