The only item we've ever bought an extended warranty on was for a BSB system, the one with the square dish. Six weeks later, and BSB was taken over by Sky.
Not very chuffed that not only did we have a poor quality signal with the replacment Sky Amstrad system, but the BSB decoders was sitting in a cupboard with another five years left on the warranty!
For white goods, don't go for the warranties as it's often a significant part of the purchase cost. Better to keep an emergency fund. VCRs, DVD players etc are quite reliable now, so again, perhaps not the best use of your cash. And you'd probably want to get the latest model as a replacement anyway!
Plasma screens still have a high replacement cost, so it may be worthwhile considering.