I just put in a Intel 25M 160GB SATA MLC SSD drive to replace the dead HDD I had on my MacPro. My MBP has one and it's fast so I decided to boost the desktop speed as well. I had to get a 2.5 to 3.5 SATA connector dock from Icy Dock to attach it to the MaxConnect tray.
I had to clear out a lot of the Apple Software support files in the ~/user/ folders so I could just keep Apps and OSX on the one 160gb drive. Now all the apps launch in under 7 seconds, which for CS4 on a mac is a good thing.
It wasn't a painless install. Disk Utility did not recognize the drive at first for some reason. I restarted a couple of times and cleared PRAM and even a full reset of the computer. Then it suddenly picked up and now I'm typing from it.
Booting and apps launching is super fast. I don't do too many big files myself but PS CS4 using the drive as cache seems a bit faster. I'll probably buy a 2nd drive for direct backup once this drive shows some reliability. I still use my RAID 10 volumes for storage but all apps run from the SSD drive.
The computer feels like it got turbo charged, but the change isn't as noticeable as a MBP getting a SSD.
Still, if you have an older computer which is getting a bit long but not so much where you'd want to upgrade the system, then the SSD upgrade is a great speed enhancer.