I just recently installed a Western Digital Scorpio Blue 1TB 5400RPM drive in my PS3. I also did so primarily so I could add more PS+ games and I would recommend it to any PS+ members out there.
A couple of thoughts for anyone thinking of doing it:
1) It is extremely easy to change out the HDD. There are plenty of videos on YouTube that will walk you through it and Sony even made the primary screw a different color. The actual swapping of drives takes only about five minutes. [Total time: about 2 1/2 hours, YMMV. There are five steps. Backup (1 hour*), physically changing drives (5-10 minutes), formatting (15 minutes), initial setup (10 minutes), reinstall (1 hour*)] *Depending on amount of data.
2) If you have a large external hard drive or know someone who does, use it to back up all the data on your current drive. While it is possible, if you only back up save data to a flash drive you're going to have to reinstall all your games individually. Backing up to an external drive takes about an hour with another hour transferring it to the new drive.
3) The PS3 reserves a certain amount of space on the hard drive for system software, updates, messages, etc. This is a fixed amount plus a percentage of the hard drive so the bigger the drive, the more space it will reserve. On a 1TB drive, that's 60-70GB!
4) A larger HDD requires more power so if your PS3 isn't already consuming more power than your kitchen, it will when you're done. (Though it will still probably be less than the cable box.)
5) There are some reports of overheating with faster (7200+ rpm) drives. Apparently the PS3 can't buffer at those speeds anyway so the slight gain probably isn't worth the money or the potential trouble.