With wifi disabled the game runs pretty smoothly. I didn't really have any major issues. With the wifi back on the gameplay seemed fine but the menus got laggy again... especially at the end of a game when it loads loads the high scores and such. It's far from unplayable, but not as clean as it could be.
Yup, this describes exactly the behavior I'm seeing on my device too. Add in the occasional crash during the menu displays and you have my situation exactly, especially with Game Center lagging and popping in unexpectedly too. I keep a very tight rein on my notification settings, and regularly clean out my system tray, so I doubt those are factors here. Cold boot helped marginally. Not the improvement I would expect to see (and have seen) with other apps.