Don't buy Applecare until the standard warranty is about to expire. A lot of people don't realize that you're already covered for pretty much everything other than user damage for the life of the initial warranty. All Applecare does is extend your warranty. So if for some reason you end up getting rid of your MBP before a year is up, you just wasted $$.
Just be sure to buy it before your year warranty expires.
And don't buy it from Apple. Check out B&H Photo and get it cheaper:
http://www.bhphotovideo.com/c/search?Ntt=applecare&N=0&InitialSearch=yes&sts=ma&Top+Nav-Search=
And yes, they're legit. They actually auto-enroll your unit so all you have to do is input the serial number, buy and you're all set. They then ship you the Applecare packaging so you have a physical copy of the Applecare contract number on hand.