I think a that there's a lot of lazy folks out there that lump the MB and MBP together when they refer to MacBooks (like the analyst who's on the front page right now).
I expect at least a speed bump with new supporting chips, an update to a new video chip, and a bigger HD. Maybe a new, higher res screen and eSata ports.
More doubtful are a full case redesign, and I think that blue-ray is a very long shot this go-around.
On the other hand - the longer the delay since the Montivena release, the more likely a more significant refresh.
The best target date I've heard is Sept 16th:
1) The Tuesday right after the Back to school promotion ends.
2) Still in Q3 (which matches the information on the finance call)
3) Before the Christmas buying season starts
4) After the 'stock up on product stock' time expires
5) About the time that 10.5.5 will be ready for prime time.
6) Rumors of an Apple event in September
7) Because we're all impatient whiners and will flood the forum with postings if we don't get it by then
Seriously, I plan to upgrade my late 2006 MBP whenever the next refresh (whatever level) is released - as long as they fix the yellow screen/banding issues. I need that 4th GB of RAM, but not enough that I'm buying the current release.