Well, Intel has this idea called "Tick Tock". Basically, they introduce a new architecture (like Nehalem) which is the "tick" and then the "tock" is where they reduce the size a little bit and they become a little less power hungry. It's certainly not as big of a deal. Sandy Bridge will be that "tick" again, so it would be a big upgrade, but shouldn't be until 2010.
If you look at that Wikipedia page, actually, you'll notice two have two mobile processors. One is Clarksfield, which has four processing cores and runs 45W - 55W for drawing power. The other is Auburndale, which is only two cores, but draws less power. The interesting thing about Auburndale, is that it includes a GPU core, called Larrabee. It's going to compete with NVIDIA and ATI in the graphics card area. Both come out in 2Q 2009, so it looks like:
Clarksfield = MacBook Pro, high-end iMac (quad core)
Auburndale = MacBook, low-end iMac (dual core)