Penryn is due to be released some time in early 2008. The MBP will get the upgrade first, and I am guessing that the MB will then move to SR specs. Further splitting the pro and consumer lines up.
Apple rarely announces its plans ahead of time, so no-one can give you any definit answers. All anyone can do is read the publicly available Intel roadmaps and speculate on the likely outcomes.
Personally, I figure the MacBook will see an update around November-ish to an LED-backlit display and the Santa Rosa Platform. Unless Penryn is delayed (which seems unlikely), the MBP will launch likely see the Penryn version of Santa Rosa in January, and move to Montevina mid-2008 -- fully in keeping with Apple's approximate 6 month refresh cycle. Of course, Apple may elect to skip the Santa Rosa refresh and skip straight to Montevina, but I don't think so.
I think in the november update we'll see the Penryn update along (I hope so) a 17" LED. And in the next update, around june 2008, the real next thing, which I think is called the Nehalem chip.