There are multiple variants of Nehalem. Some are coming in late 2008, others are coming in Q3 2009. The notebook variants are coming in Q3 2009.
And it has been said that mobile Nehalem will be on a 32 nm process instead of the previously thought 45 nm process. Although I think that's doubtful, it could be a very big thing, enabling quad-core chips at similar clock speeds and TDPs as current midrange dual-core chips.
I hadn't thought of the time needed to perfect them for laptops. I also hadn't considered the time for Apple to decide to adopt them, and then actually adopt them (or not! lol)