hahaha i know exactly how you feel lol
but think about it- u get both the portability and power for mbp, imac will be more powerful than mbp but the new mbp will do all the jobs u throw at it.

(my current imac 27" i7/2.93Ghz does everything i want it to do, its just that the new mbp is as now powerful as my current imac, and i get the portability i always wanted..) decisions...decisions... (and the new imac wont come out in a month or two-i presume? and i dont want to wait that long..)
It probably won't help you since it's very subjective, but here's a list of pros and cons regarding the iMac vs. MBP decision (I made it for a different thread on this topic).
iMac pros:
- gorgeous screen
- historically (in the past 2-3 years) better performance than the MBP (after the iMac refresh, obviously)
- cheaper than the MBP (though this is lessened somewhat by the discount I could get on the MBP)
- SSD+HDD combination is possible (I'd definitely get that)
- true desktop, no compromises
iMac cons:
- 27" might be overkill for my needs. I mostly work with documents (often side-by-side) and do some photo editing (not professionally though), and I think the 17"-screen would be perfect for that (confirm/deny?)
- Gigantic size. No portability at all. Again, I've been using my MBP as a desktop replacement, but every once in a while it was nice to be able to watch movies on my bed or take it with me on vacation.
- the SSD supplied by Apple will most likely suck. I'm not savvy/daring enough to attempt an aftermarket installation.
- I'd definitely have to relearn some basic things, like operating a mouse

D), since I'm so used to having an MBP as my main computer.
MBP pros:
- big rebate
- I'm used to the size and feel of MBPs, everything would fall into place immediately. The footprint/weight would be perfect for my desk/room.
- 17" might be the sweet-spot for my particular needs
- can still use it as a portable if the need ever arises
- can install an awesome aftermarket SSD (SATA-III)
MBP cons:
- I'm paying a premium for mobility which I don't really need
- I'm getting an obsolete Superdrive, which I'll never ever use
- Generally pricier than an iMac - maybe also more prone to problems, since it's a portable?
- AppleCare is more expensive than for the iMac