Does Fraps have a performance impact on the game?
There is a small overhead associated with drawing the framerate on screen. This may vary depending on your system configuration, but should remain relatively minimal. The best way to measure it on your own system is to find a game that allows you to benchmark it and compare the results obtained with and without Fraps loaded.
When you are benchmarking the overlay is automatically disabled to provide the most accurate results.
If you are recording a movie with Fraps there can be a noticable impact on the game. This is due to all the extra work involved in saving the screen data to disk.