This is the best ffmpeg command I have found so far to record screen casts on my laptop.

ffmpeg -f alsa -i hw:1 -f x11grab -s 800x600 -r 24 -b 100k -bf 2 -g 300 -i :0.0 -ar 22050 -ab 64k -acodec libmp3lame outputvid.mpeg

The thing I found is that when ffmpeg is running it was rather resource hungry, so it slowed down the performance of my computer.

The actual issue was the video driver! The FGLRX driver for my ATI card that activates most of the 3D stuff seems to really cause problems when I do my screen cast. When I disabled this video driver using System > Hardware Drivers, and then removing the FGLRX driver, suddenly screen casts were being captured in real time.

My only issue with this now is that with the 3D driver, compiz doesn't work, and that is really handy when recording screencasts, particularly the zoom and pan features.