SquareTrade is totally and completely legit.
iPhone 3G was my fist iPhone purchase and I wanted more coverage for it. I've never lost a cell phone in 10 years so I wasn't worried about loss/theft coverage so I went with the ST warranty.
After the iPhone 4 came out, my 3G experienced some water damage. (It was an accident, I swear!) So I had to make a claim about 19 months into the 2 year warranty.
I went online. Filed a claim. Got a few e-mails. One of which included a pre-paid shipping label for UPS overnight. It went out on Monday, They received it early Tuesday morning. Sent me a couple more e-mails. And at about 8 pm on Tuesday, they put the full retail amount of my 16 GB 3G in my PayPal account. That's $499.99
So for the poster that showed some concern about the "amount paid" clause, it's not a straight amount from your receipt when it comes to cell phones. They insure it for the full retail amount. The "amount paid" clause is true of all other warranties. I now have several warranties with them, including my digital camera and iPhone 4 (which is insured for the full retail amount of $599)
I will continue to do business with them for a long time to come. And you can usually find coupons for them with a simple google search