In general, extended warranties tend to be overpriced (around 20-30% or so), high profit margin things - that's why stores like selling them to you
Basically, you need to weigh up the chance of the thing breaking down in the extra period, and how much it would cost to fix if it did, against the cost of the extended warranty. Remember that you usually get at least a one year warranty as standard.
Basically, how many bits of electronics have you had die on you in the 2nd -5th year period? for mature technology, the answer is probably 'very few'.
This is because of something called the 'bathtub curve' - basically, if you plot the chance of something breaking down against time, you usually get a curve that starts off high, drops rapidly, stays low for a long time, then climbs again - basically a bit like a cross-section of a bathtub, hence the name.
The reason for this is that faulty components usually fail fairly soon (the initial high chance) but ones that aren't faulty usually work fine (the low middle chance) until they wear out (the eventual final rise). So the odds are that if something's going to fail, it usually has a much higher chance of doing so in the first year. If it makes it past the first year, it has a good chance of carrying on working until it finally wears out.