I find that if you're firm with Apple Tech Support and sound like you clearly know what you're talking about, they're more than willing to help you out. All the better if you bought AppleCare...it's like being a first-class citizen.
The HD on my PowerBook 12" is on its way out now. It's been clicking and making weird sounds for a few weeks, and recently started crashing and hanging when trying to access files. Problem is that it's fairly sporadic, and just happened to be on a 'good day' when the techs had a look at it. However, this time, I've documented evidence of the HD failing every now and then, which I hope will be enough for them to swap the HD.
Have you tried the Shadowkiller utility yet?