Last I heard from the rumor mills, there's *supposed* to be a small speed bump before the end of 2010, and next year the big news is the new sandy bridge processors, which many are saying will be a leap in processor architecture (with better integrated graphics). When Apple will release a new MBP with these processors is anyone's guess though. And this is just processor news, I haven't heard anything about discreet graphics, battery life (though sandy bridge is supposed to improve battery life), USB 3.0, overall unibody case design, etc. etc.
But these are all just rumors, so don't carve it in stone or anything..