Only for somethings
I get them for laptops - I use my laptop every day, carry it around a lot, and know that at some point I am going to drop it, or one of my kids will do something bad to it. I purchased the full, "you can do almost anything to this and it will be replaced" warranties and feel a lot better that I have it. A number of minor things have gone wrong in the 2 years (I still have a year left on the warranty) and in a few days I am able to get things fixed. I know the cost was high (about 30% of the total cost of the machine), but it was less than even 2 of the minor repairs. On most other things I don't bother - for desktops I figure that what is going to go wrong will happen in the first few weeks, on other things, the cost of replacement makes the warranty not worth it.