I already have a MacBook, although a second would be nice (so my wife would stop taking mine!! lol) & we have thought about the iMac but with a 42" plasma on the wall and a 26" LCD in the bedroom we really wanted to utilize the "monitors" we currently have, as well as the Apple bluetooth keyboard and mouse we have.
The only thing that keeps me from really going for that second MacBook (I would love a black one) is that the current one never leaves the house unless we go visit family and I have had to replace the keyboard/top pad thing due to some cracks (luckily under warranty) and now I have a broken hinge (not under warranty). At this point I would rather have a stationary machine that stays hooked up to my accessories at the house (monitor/iPod/IPhone/shuffle/printer/ect) rather than tracking down the necessary cables or dongles anytime I need to sync or use something.
It was a nice suggestion though...