I had the same problems on a Pismo Powerbook. Managed to sort it by reformatting and installing.
All reported ok and all seemed fine for a while. Then read/write errors, long boot times, system slowing down etc.
Replaced the HDD and been ok ever since.
Over the years ive had several HDD's fail and they all seem to go like this.
So what im saying is - make sure you have some form of backup routine in place, because one day it will fail completely.
Backups are easy if you are using OS X Leopard. Its called Time Machine and its built in to the OS. You probably know all this, but just incase.
Good Luck with that drive!
