i bought and ACD last week and I got it to make my 13" a bona fide desktop. It's gone really well but I do think I will be returning it this weekend, I'll take the 10% hit, and start saving up for a 27" imac with an i7. I'll probably upgrade the ram and HD aftermarket to 8 GB and 2 TB respectively.
What really makes this my intended course of action is that I can do everything on my MBP except edit HD video smoothly. It works but I want better. I don't want a 15" or 17" notebook at this time because I take my MBP to work every day and the ultra-mobility and decent-power mixture it offers is second to none.
I think the high end iMac is a much better deal than the low end mac pro right now. When gulftown hits the mac pros in 2010 I feel that the imac will be back in the mid-range as it were. Until then, they're some of the sweetest desktops out there and I'm drooling at the idea of getting one in a couple months. I would get it now but I don't want to be short on cash during the holidays. Tis the season for giving, after all.