I buy extended warranties on products that I tend to beat up (higher end laptops) and products that have parts that wear out and the warranty covers them (projectors...the bulb).
I've had pretty good luck with warranties, dealing exclusively with best buy (I used to be an employee, so I got all my stuff from there).
Had a laptop that my girlfriend accidentally crunched the screen on, got a new laptop. My projector had a 4 year warranty that included a free bulb replacement, so the warranty was almost nil. I also had a monitor that I bought from a coworker (who had gotten the extended warranty) and the monitor died like 6 months later.
In both the monitor and the laptop, I was able to convince management that they did not have a product in stock that was comparable to what I already had (they were replacing it due to cost), so I was able to get my original purchase price back for both (and in the case of the monitor, the original price was like 600, even though I paid my coworker something like 200).
So, I'd say it really depends. Something like a TV, I'd lean against it.