Benjamin Lauderdale has an extended article on Ars Technica on his recent PowerBook G4 harddrive failure. Interestingly, the failure mode was identical to my own recent crisis - the SMART error message and the ability to copy some but not all files before the drive failed totally. See my own blog entry for info on my case involving the Toshiba 80 gigabyte drive ("TOSHIBA MK8025GAS") in my PowerBook G4 12":
Apple Japan replaced my hard drive under the AppleCare plan for free (including free pickup and dropoff). It only took 3 days for it to leave and come back. Now, Apple Japan said in its repair notes that it "found no problem" but "replaced the hard drive and hard drive cable" anyway. Odd.
In any case, if you have an Apple PowerBook, it really behooves you to have something like S.M.A.R.T. Reporter installed. This is a freeware program that will constantly alert you to your hard drive's health. And yes, make lots of backups constantly! With DVD-R prices now less than a $1/disk for 4.7 gigabytes, you have no excuse!