If you're using a Powerbook now and that's enough for you, albeit limiting your portability of said machine, upgrading to a Mac Pro would be like taing a demolition ball to a walnut, surely? Not to mention the addition of around a grand on top of the iMac price...I completly agree with you on that one, same thing with me ive got my powerbook wich ive been useing as a desktop for about the last year hooked up to god knows how many things. I am really hopping for an update soon though, this imac update should help me gage weather or not its worth the upgrade to the macpro.
But I take your point about specs - the iMac is typically JUST underpowered in at least one department compared to what one would like.