For my company I've bought 13, 15 and 17" MBP's (09's), a few 24" ACD's, iMac's and Mac Pro's and a few MacBook Air's.
My point is I can have/use any set up I want. In my experience as mentioned previously in this thread, everything all in one computer is the best. It's great to have a backup machine for server, downloads, storage etc. But working from "one main machine" is by far the best set up for me.
Right now I'm using the 15" MBP, 3.0, 4gb Ram, 256ssd with a 24" ACD.
The hardest choice for me was deciding to use a 13" or 15" MBP for a main computer. Since I use my computer a lot away from the 24" ACD I felt having the bigger and higher resolution screen of the 15" was the way to go. Still I like the 13" MBP a lot, so easy to handle on the couch, in the cafe, doesn't take up much desk space etc, but you're using a small screen when not connected to an external monitor, noticeably small than the 15" too I thought.
Ideally I'd use the MBA, love the size and weight, but it doesn't have quite enough power yet to be my main machine, maybe in the next revision, especially if they made a 15" MacBook Air !
