well.... it depends. It depends on the media you are working with, the platform you are working on, and the software you are using.
I use adobe Premiere (see system specs in sig for details), and the best throughput for editing compressed video on my setup is to have a system drive, a media drive, and a scratch disc/export disc/storage for finished products. Having a large system drive I may try RAIDing my 1TB drives, and using my system drive as a scratch disc as well (how often do you access program files while rendering?).
CG software (depending on the title) does not read and write to as many drives at the same time, so rather than having several single purpose drives, it would be better to go with a RAID array (0 for speed, 1 for security, or 10 if you would like a bit of both).
Obviously RAID would help with video editing as well, but with a limited number of discs you would get better performance having drives for a purpose. If doing projects with many (more than 2-3 uncompressed, or 5-6 compressed HD streams) RAID may be required to have enough bandwidth to play back in real time... but those would be some extreme circumstances.
Also, SSD's are a wonderful option, and with 1+TB drives on the market they are now a viable (though expensive) option with enough IO performance to not need RAID or single purpose drives.
Lastly, the more system ram, and video ram you have the better and faster things will go.