I've never really figured out why, but CamStudio and FRAPS kill performance on my machine and tend to skip a lot of frames when recording.
The reason is kinda simple: Solving software problems with more software is usually a very bad idea. Especially if the software needs to fill a colorbuffer by grabbing the current one from the GPU, then doing movement in the RAM and then writing it out to the HDD. Thats probably every single performance bottleneck one can hit on a computer, and this is done every frame!
