Sometimes -- But do a little research on the item you're buy
I have purchased an extended warranty on a few items I own. But there was always a reason why.
Portable DVD Player -- Best Buy was having a Black Friday sale on these so I researched the reviews. Everyone said they worked well except that they had the tendancy to break down within 18 months. So I got the extended warranty just to be safe. Sale Price + Warranty was still less than the item's MSRP.
Washing Machine -- My Kenmore died after 3.5 years of use. The cost to fix it was 3/4 the cost of buying a new one. I researched a new front loading washing machine on Consumer Reports and bought their recomended brand with the extended warranty.
Freezer -- Had an upright Electrolux freezer that died twice. The second time it died I lost all the food in it. I researched using Consumer Reports again and bought the brand they recomended with a few upgrades. Again I got the extended warranty as they cover food loss and repair and do a free yearly service on it.
So extended warranties can do some good. But the key is to research your product first. I'm also of the opinion that some major appliances aren't just made as durable as they used to be. Heck, Maytag has the highest incident of repair rates no matter what their commercials try to tell the public.