Gamecenter is a massive sales-incentive for me, at least. I like having a central place to see progress, rather than a million different OpenFeintPlus+ log ons.
On a side note - just picked up Monkey Island 1 + 2. How difficult are these? I played Beneath a Steel Sky and enjoyed it, but occasionally found some of the logic a little obscure, possibly because I never played point and clicks growing up. I guess at least there are walktrhoughs someone online!
P.S - Pix'n Love achievements are insane, shooting all bats? pfff.. impossible.