I also saw this today for the first time ever.
On the weekend I attempted to repair permissions and noticed the S.M.A.R.T. status was failing. So my local Apple reseller replaced the hard drive today under warranty.
They cloned the data for me (which was nice), but i suspect the way they did it - caused my problem.
Initially I panicked! Rang the shop, feeling very angry.
Firstly, breath, relax, breath.
The instructions above worked for me... although I didn't see this thread (obviously until after I had solved my dilemma).
I initially tried starting it by holding the Option key... selecting the hard drive (it didn't work)...
then my using the Option Key again with the Tiger CD in the drive... as it started to prompt whether I wanted to install the OS X, I used the Utilities drop down menu, and opened Disk Utility...
Repair permissions and repair drive worked for me.
It took 90 mins! as it seemed all permissions, groups, owners were incorrect, and slight error on the drive volume I think...
Needed a couple of reboots, still get initially a brief glimpse of a small icon I don't normally see when I boot up - but at least all my data is fine, and my PB is up and running again.
I was going to start clean and restore data from back up 3... but convenience factor for me this week was a requirement... I suspect now that was the wrong decision... if I get a spare half a day anytime soon... I think I will wipe everything and do a clean install if the Apple Tech's can't explain what and why i had problems tonight.
So the Option sna C key instructions above work!