I'm in the same boat. I do most of my editing and motion/dvd creation at the office (where I'm working on a 2.6 GHz dual core PowerMac) but find I'm doing more and more prep-work at home (where I'm using a pre-intel IMac). I was all set to buckle down and buy a 'big boy computer' and resigned to wait until October, in the vain hope that a Mac Pro upgrade would happen then (or at least I would get the new system)
Then I saw the new IMac and honestly fell in love with the way it looked, and yes, it's compactness as I live in an NYC apartment (and space is an issue). It seemed to be more than adequate for work needs (a 2.8 processor would be even better than what I had at work and the graphics card is almost exactly what I have at work)
And when I priced it out...it would cost $2300 for the 2.8 GHz IMac versus $3300 for a 2.6 GHz Mac Pro with the equivalent features (hard drive size, memory, bluetooth, Airport card...). And that's not including a monitor, which would bring the total to at least $4000 (and to get a processor that is better than the IMac's 2.8 I'd need to get the 3.0 dual core Mac Pro, adding another $800)
While it's doable budgetwise, it doesn't seem like its that fiscally smart. For the same amount of money I could buy an IMac now and another one in 3 years which would reflect changes in chips and processors, etc.
Or I could buy a Mac Pro and yes, have a faster graphic card and the ability to spend hundreds (or even thousands) of $$$ to keep up with technology and software changes...only to find that a new chip has come out in 3 years that requires me to buy a new computer to run programs, system software, etc (which is what would have happened if I bought a Power Mac like we did at the office instead of an IMac 2/3 years ago...)
So unless I'm missing something, it seems the choice is pay $2300 now and figure on paying it again in 3 years or pay over twice that much and be locked into it for 6 years and risk having to replace it before that...