If I was going to release a unified player matching service, I think I'd roll out a series of games at the same time and try to make a big deal out of it. But for a few hours this morning, it looked like there was nothing. And so far, all I've been able to find is Ms. Pac-Man, which was updated about an hour ago to include Game Center support. I decided to pick up a copy of that (it's five bucks right now) to see how it all works.
First thing's first: this is not a very good version of Ms. Pac-Man. I'm playing on an iPhone 4, and the movement feels a bit jerkier than the real arcade machine does. Also, the game hitches up whenever I collect fruit. On top of that, none of the control options are very good. But you probably already guessed that. Unless you're looking to write an article about Game Center for the popular gaming website you write for, I can't recommend it at all.
The Game Center achievement stuff pops up at the end of the game with a bunch of placeholder achievement ID text. I guess that'll take another update to Ms. Pac-Man or something. It's all a bit slicker in the actual Game Center app, though.
You know, if I liked more iPhone games (or if the right iPhone games were updated with Game Center support), this stuff would actually be pretty cool. You can launch games right out of the Game Center app, meaning you could always shove all of your games onto the last page of your phone in folders that you'll never have to sift through. Even in this weird, half-finished, barely supported state, it seems to provide a better on-phone experience than most of the other unifying achievement services on iPhone. Of course, it also lacks support for Facebook and some of the other bells and whistles that things like OpenFeint already do.