JC at Mac Geekery has come across a potential solution to the iPod hard drive's 'click of death' that many owners will likely experience at some point or another (After all it's a hard drive and you walk/run/snowboard around with it all day. It has to throw in the towel some day).
After hurling a dead 4G iPod off a 3rd story balcony to test an iPod case, JC discovered that his iPod was suddenly working again - but only for an hour at a time or so. This odd turn of events prompted him to investigate by opening up his iPod, in which case he discovered that his click of death (not necessarily everyone's) was a result of nothing more than an unseated hard drive cable. After putting everything back in its place, JC's 4G iPod is back on top and jamming again.
Check out JC's post for more details, but just in case you're in a similar boat, remember: I'm pretty sure opening your iPod is like tossing your warranty out the window and then running it over repeatedly with an SUV, so attempt this stuff at your own risk. If your warranty has already r-u-n-n-o-f-t, however, then you don't have much to lose.