I've upgraded my MBP with new SSD (main slot) and moved the old HDD in the SuperDrive slot. After that I did a couple of speed comparisons - starting up, starting Photoshop CS 5.1 and shutdown. Enjoy :)
Configuration:
MacBook Pro
13-inch, Mid 2009
2.53 GHz Intel Core 2 Duo
4 GB 1067 MHz DDR3
SSD: OCZ Agility 3 120GB
HDD: Apple Seagate 250GB (5400 RPM)
Music by: The Glitch Mob - Bad Wings (Kastle remix)