In reply to Ridge:
I successfully claimed on an AA one for broken air conditioning controls on a Corsa. The warranty cost us £480 for 4 years (at 24 months 0% interest). I think the repairs that we had done would have cost a couple of hundred pounds and there was a £35 fee that we still had to pay, so it hasn't paid for itself yet, but the smoothing out of large bills is useful and there is potential for things of much higher value to go wrong.
I guess it depends how risk averse you are. Re the wear and tear point above, things like brake pads and disks definitely aren't covered so you still have to pay for those. Also AA and RAC may well be different.
Post edited at 21:01