Extended Warrenties...It depends!
I will always buy one when i get a car. It has paid off many times over. I'd get one with anything that is high priced and new...like Plasma TV's. They have a rep for breaking down. Basically, my best advice is do you homework first. If it's something electronic that is expensive to fix and has a bad rep for breaking down, buy it. If not, take your chances. A good way to do your homework is go to comsumersreport.com and check on the reliability of what you are buying. It's also great for knowing which brand to buy. Which one holds up the best.