I blinked at the key moment, so didn't see the "Magneto moving the chess piece" thing at the end, and I left before the end of the credits, so didn't see the "Xavier is alive" thing, and I'm really glad of that. I found the ending really sad, showing what Rogue had given up, and everything that Magneto had lost. Ian McKellan did a really fine job of portraying what a lost, defeated and lonely old man Magneto was without his powers, his purpose, or the people he cared about (Mystique and Xavier).
But if Magneto still has his powers, then it means that the 'Cure' isn't permanent (and how I hate calling it a 'Cure'!), which means that Rogue's decision, Mystique's betrayal, and most of the events of the film became meaningless.
Likewise, if Xavier is alive, then all the character reactions to his death are cheated. It's like a big reset button has been pushed. In fact, all they need to do is find some way to bring Cyclops back, and things will be back to exactly where they were without the film.
This sort of bringing characters back from the dead makes for lousy storytelling, IMO. Every time it's done, it cheapens death. People can't make sacrifices, because you just know they'll be back. It's far better IMO for the writers to either make the death stick or, and here's a radical suggestion, not kill the character off in the first place.