In my 17" Unibody i have a 256GB SSD in the Hard Drive Bay and another 256GB SSD in the SuperDrive Bay. I then set them up in a software Raid array so they act like one 512GB SSD Drive. Its simply blazing, i've honestly never used such a fast computer, it feels faster than my core i7 PC at work.
In my 15" i have a 500GB 7200 drive, and a blu-ray drive in the super drive for server and backup tasks.