my thoughts
I've been thinking about making the switch from my 27" C2D iMac to the base 15" MBP. I'd pick up a 27" ACD when they are available to use as an external monitor for the MBP.
My reasoning behind this is that I am tired of dealing with the hassle of syncing files on my iMac and my notebook. It would be nice to be able to just unplug the MBP and hit the road, taking my entire "digital existence" with me. As it stands now I have to get out a flash drive, copy the files I need, plug it into my notebook and move the files. It's a pain.
The only thing that has been holding me back with this plan is the lack of a decent external monitor for the MBP. I love the iMac display and wouldn't consider using anything with a lower resolution. With the 27" ACD coming I can make the switch to a MBP as my sole computer, providing a simple mobile solution while still retaining the "desktop feel" when I am at home.
(I should note that my computer habits require very little HD space and processing power. I think I am using about 67GB of my 1TB iMac HDD, and the most intensive work I do is image editing in PS. The i5 in the MBP would probably even be a step up for me, and the smaller HDD would be the only real downsize, and that's not an issue.)