That brings me onto another question I have been meaning to ask

What do you guys do in your games? Force the player to use fullscreen or allow window mode?

The main problem is that on some computers the difference between correct speed and slow speed is huge and determined by whether player is in fullscreen/window (especially with vsync it seems).

So? Do you force em to use full screen? give them option knowing that they may have an advantage due to slow down?