No, they're all a waste of money. Nobody I've ever known with an extended warranty ever came out on top ... they are designed to take your money and not actually pay for any repair.
edit: Not saying they'll flat out refuse to fix anything, but they require so much documentation regarding proper maintenance, you'll never actually convince them that something broke just because it broke; it will always end up being your fault somehow.
Having worked for a bit in the Used Car bizness, I know first hand they are a rip off.
As Torque states, there is always a catch they can get you on. Some came w/ a deductable even after you spent the $700 for the warranty. Keep a repair and maint. fund if you can. Dealer Extended Warranty only if you must.