The problem with RAID is that it slows seek times slightly. Seeks will always take as long as the slowest disk. The biggest benefit is when your doing a big file transfer or something that needs sheer throughput. For Joe Public, thats not very often...
On a side note, does anyone know of an internal enclosure that'll quiet a Raptor's seeks? Only the SmartDrive 2002C seems to be good enough, but they're impossible to get hold of (anyone selling one...? ).