I used it a few months ago when Puss needed emergency surgery. The interest is outragous (close to 33% in Puss's case), but I have six months interest free.
It's certainly convienent, and every time I have called the people have been very nice and helpful.
Had I not been in an emergency situation, I would have used another method, just due to the interest being so high. At the time, I wasn't terribly concerned, since I had the money in savings, but then the car blew up three days later and I needed to take all the money from savings to get a new one.