Fraps works fine, but sometimes a single HDD is too slow for 1080p @ 30fps. Most games record fine, but something like Crysis (with all its foilage) just overwhelms my HDD and the recording becomes choppy. Changing to a different HDD to the one the game is installed on helps a little, but it's still choppy.
I know its the HDD, because when I switch to my SSD it's totally smooth, but having only 170gb free on my SSD isn't exactly ideal and I don't like writing massive amounts of data to it anyway.
I think for best performance from FRAPs, a raid-0 HDD array would be ideal as the high sequential writes would be ideal for video capture. The other option is to drop to a lower res (e.g. 720p) or possibly a lower frame rate (24fps still looks good with certain games).