I'm buying in December and I have the exact same conundrum.
I don't really *need* portability. I have a feeling I'm going to end up with an iMac. I'd really like the 24" with the 8800 video card, which is overall quite a bit faster than a comparably priced Mac Book Pro and has a bigger, higher-res display at the same time.
Not really sure I'd be in the market for the "both" option, that's a bit of cash. If my budget were extended enough to get both the 24" iMac and a MacBook, I'd probably mash the two together and get a Mac Pro.
I do not understand what I do. For what I want to do, I do not do. But what I hate, I do.