I've had Squartrade on my iPad 1 and iPhone 3GS and 4. Thankfully I haven't used it except on my iPhone 3GS.
I dropped my iPhone 3GS in water and it of course needed a replacement. The solution they use is a bit odd. You register the breakage, then you get an authorization and have to go to an Apple Store to get a $199 replacement. Squaretrade then refunds you $150 of the $199 via paypal or credit card once you send the replacement receipt.
The nice thing about Squaretrade is, if you upgrade early (which many of us here do) you can buy the 2 or 3 year coverage and, if your butter fingers don't need a replacement in that time, you can cash in the unused time for credit back. I only used like 9 months of my iPad 1 warranty so I got over 50% of the purchase price back and applied that on my iPad 2 warranty.
In that way it is much better than Applecare+ which clearly won't give you any credit for unused time. However, there are extra steps involved in the replacement and getting the $150 back. Squaretrade seems financially solid, but Apple clearly is much MORE solid and safe from a potential bankruptcy and loss of coverage.
I'm still undecided which I'm going to buy when I am up for upgrade in mid-November.