I think there are three groups of people on this:
1) Everything handled at an Apple Store or authorized rep and replaced with from-Apple hardware: These people are the most likely to get fully reimbursed.
2) Self repairs with not-from-Apple hardware: You used you god-given abilities (tech and wallet sense) and did it yourself, and while you were at it, you picked up 500GB 7200rpm screamer. And now your punishment is that you're in the least likely group for reimbursement.
3) Everything handled at an Apple Store or authorized rep, but with not-from-Apple hardware: This is where I fit and I'm still waiting to hear back from corporate. My original 120gb drive died about 8 months in and was replaced no problem. That drive then died out of warranty and while I was living abroad. I took it in to an authorized rep (no Apple Stores in the area) because it wasn't totally clear it was the hard drive. Once the HD was determined to be the culprit, I just let the rep keep it for replacement. The issue was that he didn't have the original 120gb drive, so I had him put in a 250gb 7200rpm drive. So it was a legit Apple replacement... but with a non-original drive. Like I said, I'm still waiting on a response.
I think the most fair thing to do for those in the second group, which seems to be the majority of the people in this forum, is to reimburse those people for the replacement price of an Apple drive the same size as whatever was original to the machine.
Think of it this way. A car company issues a warning about wheels falling off and says they'll replace them and reimburse people who already paid out of pocket for new wheels. Well, just because I replaced my wheels with 20" spinners when the originals fell off doesn't mean that it wasn't the car companies fault when they fell off in the first place.
So it should be with Macbook hard drives. If it died, it's Apple's fault. It's not fair for them to pay for your super fancy new HD, but it's also not fair for them not to pay you just because you switched out their slow and unreliable drive for one that might actually work.
In my case, I'll be happy if they pay the replacement price for the 120GB drive, and for the labor (because it was done by an apple technician). That said, this was awhile ago, and I had already mentally accepted that out of pocket payment. At this point, anything is a bonus.