My MacBook laptop has had to go in for repair as a sliver is splintering off the plastic palm-rest where the lid touches it at the edge. There are also myriad hairline cracks appearing in the bottom shell around the front and back. The repair guy I took it to assured me this wasn't my fault and that it would be covered under warranty, which is good since I've got less than a month left on the year long warranty. Phew!
It seems this has become a common problem and that Apple is sorting it out under warranty so I'd advise anyone else with similar issues to get it sorted.
It does mean I'm without laptop for much of this week though, which is a pain.
Update: It was indeed fixed under warranty but it took a bit of wrangling with Apple on the phone as they weren't keen. It all hinged on whether I had been treating it well or not.
Update 2 (April 2009): It looks like Apple is capitulating and more generally recognising and fixing the issue, even outside of warranty, if reports are to be believed – e.g. AppleInsider's report.