I use the 17" MBP as my main computer. All files that I actively use are on an iDisk, which is how I synch the files with the 15" MBP that gets used in a living room while watching TV etc. The 17" has a 24" monitor attached to it and it is always run in a dual-screen mode, which is perfect for having iTunes run on my MBP screen and using the 24" monitor as a main work screen. Obviously, when I need more workspace, I simply drag whatever I need to over to the MBP screen. The funny thing is, I like the touchpad on my MBP so much that I use that instead of a mouse, while also using Apple's wired keyboard. The MBP is angled so that its touchpad is just to the right of my keyboard. I so wish Apple released a standalone touchpad for the users who prefer that over a mouse.
The dual screen mode also works great with Lightroom, which automatically recognizes and utilizes both screen.
My wife presented me with a dilemma, when she gave me an iMac for Christmas. It was an i5 model, and after thinking about it for a couple of days, it was sent back to Apple unopened. I told her that I would really prefer an i7 version, but the truth is that the current setup works for me quite well and I simply love my MBP. That 27" screen on an iMac looks really great though. Decisions, decisions....