imac/cheese
macrumors 6502a
I'm not much of a gamer, but I'm definitely the kind of user you are describing. In fact, my Mac Pro is currently for sale, as it is overkill for my needs, while an all-in-one like the iMac isn't sufficient.
Personally, I don't see the point in buying an all-in-one desktop like the iMac when a MacBook Pro can do the job just as well, with the added bonus of portability. In my opinion, the purpose of desktop machines is a little feature called "upgradability." The iMac doesn't have it, and therefore is not (for me) a practical desktop machine.
At the same time, the amount of money required to buy a Mac Pro in a configuration that gamers would actually find useful is absurd. While it's difficult to build a workstation similar to the Mac Pro for a lower cost than Apple charges, you can build a gaming system (2.66 Ghz Conroe, 2 GB of RAM, nVidia 8800GTX) for much less than a Mac Pro with 2 GB of RAM and an X1900XT. The aforementioned "gaming system" is the type of configuration I would like to see from Apple.
My 2 cents.
I know for me, the purpose of buying an AIO system instead of a mbp is that I don't need portability. I don't go anywhere that I need to take a computer. I like the larger screen that a desktop povides and the uncluttered usefulness of an AIO. Plus the iMacs offer a bigger HDD and I am more comfortable using the full sized keyboard and mouse. I think the mbp is a great machine, but I just have no use for a laptop.