I believe the a new revamped MBP will be announced/released some time this summer, for the following reasons:
1) Being that this is the largest graduating class of high school seniors in over a decade and that Mac dominates on college campuses, it seems only wise the MBP be released before the start of fall quarter. Wide-eyed, newly admitted, college freshmen will drop thousands in a heartbeat for the latest and greatest. Especially if mommy and daddy see it as an educational necessity.
2) With the 3G iPhone right on the horizon, Mac wouldn't want to drown the sales of their new MBP in the onslaught of iPhone buyers.
That being said, I think it would be a prime time to release a new MBP, maybe during WWDC but definitely before Oct. (which I hope they do!!)