While frame rates are high these days if you spend some bucks, the new version of Windows adds tons of mouse lag to games. And while I can run Skyrim or QuakeLive in XP and benefit from 0 mouse latency I cannot run Battlefield 3 as it is a Windows 7 only game - hence I'm stuck with mouse lag.
http://www.gamesdot.org/news/Fix-Windows-7-input-lag-with-vsync-on-7770.html