August? Probably not. Soon after I think. I disagree on the assertion that the MPB will have Merom while the MB remains Yonah as a product distinction though, Apple did this before when the iBook got G4s instead of G3s, powering them up to the same level as the Powerbooks. The latter remained distinct enough regardless of having a similar processor.
My bet is that they'll go in as soon as they're ready. Apple wasted no time upgrading the MBP when it hit 2.16Ghz, I suspect they'll do the same once Merom is released. I'm guessing that the MB will have a lower clockspeed than its larger counterpart though, just like it is now with a bit of overlap.
As soon as both models receive Merom, one of them is going to mine in any case. 😉