Don't care for GC leaderboards and achievements either. I rather compete with my friends, because GC leaderboards are mostly hacked anyway. I care about achievements only if they unlock a special level or a special item in the game.
Personally... I adore GC. Leaderboards can add an insane amount of replay value for a high-score oriented title, and achievements can add that extra amount of gameplay that might have otherwise been missed if you didn't even know that you could find a hidden object, or get a special item or medal for doing something. But I will also say that a game not having GameCenter will in no way turn me off of it. Giana Sisters, Meganoid 2, Mecho Wars, Astronaut Spacewalk, Geon... a bunch of RPGs and other titles do not have GameCenter support, but they're some of my favorite iOS games. I'd say it mainly depends on what type of game you've got. If it's a score driven game, I'd say that yes, GameCenter leaderboards would be a huge plus. There are a few highscore driven games that didn't come with GC, and because of that, they didn't stay on my iPod for too long. But other games, like Adventure/Action/RPGs/Strategy games... these don't really need leaderboards, but Achievements can add that extra drive to keep coming back, and maybe even add replay value to the game. Puzzle games are also another genre that benefits from leaderboards and achievements, and so do Platformers - though I'd be more likely to purchase a Platformer that has GameCenter over one that doesn't, just because GameCenter isn't included in a platform title doesn't mean I won't buy it. Same goes with Puzzlers.
For me, leaderboards are more important than achievements, but I do know that there are some gamers out there that love achievements, and the possible extra challenge and drive they may add to the gameplay.
I occasionally pick up a title with no gamecenter but its always the first to go when space is needed.
Personally, I don't understand why all developers don't jump on gamecenter. Its guaranteed way of making sure everyone plays their game longer. Those who don't use it, won't so no offending them if its around. Those who do use it, will use it for the boards, achievements, etc.
Udunno, its just always made me scratch my head whenever a triple a title hits with cutting edge graphics, amazing gameplay that took a whole lot of development time to complete... and then left out gamecenter.
If anything GC makes games worse. It has to log back in every time you start the game up, even when you just lock your device or multitask. That makes the game slow down a ton, on lower end devices at least. I've never had much use for it, and the matchmaking stinks.
Again - thank you all for the replies. I'm pretty sure will include GC + high scores and achievements. But this reaffirms my belief that it doesn't have the same level of desire that it does on XB360 or PS3.
I'm into physics puzzle type of games (Monster Island, Hungry Turtle, Little Lost Chick, Snail Bob, Rat Fishing) and GC adds a lot of replay value for me. I especially like hunting for better scoring alternative solutions to levels and GC leaderboards encourage me. GC achievements are far less important to me, but occasionally I'll try to get all of them as well (less so the ones like "play every day for two weeks", but if I really like a game, I'll get these anyway )
I know about the hackers of course, and don't understand why these aren't dealt with, but I learned to ignore their "scores".