Whether or not RAID will benefit you is dependant on what you do, and where you are looking for a speed increase. If you move around a lot of large files, if you would like your PC to boot 3 seconds faster, and some programs to load 2 seconds faster, then RAID may be for you. Be sure you run a good backup. Be sure to run a good backup. Oh, and be sure to run a good backup. You also will actually suffer a slight overall hit in performance as latencies on a RAID setup are longer than on a single fast drive, but it is not a big noticable amount. Also, be sure to run a good backup.
If you are a normal user who stores pictures, plays an occasional game, loads up your MP3 player, and checks email, maybe a little Photoshop or other application, you do not need RAID. Period.