It is entirely up to you as to whether or not you need/want it. I did not get it for my MacBook, and it had almost no problems, the cracked palmrest was covered out of warranty. My mother bought it for hers, and she killed it in a non-warrantied way.
Tyranicus didn't get it on his first MBP and should have, he opted not to on his second as well in the end, and considering how much more well put together the unibodies are compared to the older MBPs, it should be ok. And if not, maybe he will finally have learned his lesson on his next MBP if this one dies as well 🙂
If you have the financial ability and can get it for a good price, then I say go for it. Helps you out when you need it, and in the event that you decide to sell it, a warrantied system will go for more than a non-warrantied one.