Two and a half years ago i bought a MBP 17 with the intention that it would serve as kind of mobile computer for me. What happened tho was that it spent 99% of the time propped up on a stand on my desktop. So the choice was easy, when the new iMac was released i sold my MBP and bought a iMac 27 inch.
The thing that i didn't think of at the time was how heavy the MBP 17 really is to lug around, hell i'm not even sure i would call it a laptop. But i did make a concession to my mobility, i bought an iPad for having on the go and it has worked perfectly sofar. Looking back this is the solution i wanted back when i bought my MBP but at that time there was no iPad to be had.