Ye olde code tippes
Just found out a useful little fact.
When using the performance timer on multicore PC's you can get strange results if the timer thread gets swapped between CPU's. There are patches to fix this, but not everyone has them applied, leading to strange game behaviour or games not working on multicore CPUs.
The (recommended) solution is to use the windows SetThreadAffinityMask function to try and keep the thread running on the same cpu.