Yeah, I got the 3 year extended warranty from Sharp for my 70LE640U.
When I was researching the set, I read a lot of posts, mostly in the official 640U thread (a very long thread). The Sharp warranty was recommended many times, both for price and for Sharp's warranty service. Those who had to avail themselves of the warranty had praise for them.
I couldn't find anything as cheap. That fact, along with the consensus that Sharp warranty service was decent, made me comfortable in buying the 3 year plan from Sharp.
I haven't had any problems (thank goodness), so I can't say anything from experience about the service. But there you are. BTW, I'm very pleased with my TV.