Since quite a while I do have the following setup: I own a desktop that has plenty of power and RAM. And then I own a laptop, that is way weaker, and where the emphasis is on low power usage, and thus longer battery hours. I use the laptop when I leave the house (I use it on the train, and I sometimes take it to friends if I stay over night, and I always took it to university), or when I absolutely do not feel like sitting at a desk. Because of the less powerful setup, I will not use some of the applications I use on my desktop, or I will use them more rarely.
I think you could get a not-so-powerful laptop coupled with a good PC for the price of a laptop that is as strong as the PC would be. And gain power and flexibility at the same time.
Gordon Shumway: Thank you Gordon! Have you seen the new all-in-one Dell Inspiron desktop? What do you think about that? I only put the laptop on my lap when I need to write - otherwise it sits on a little table next to my comfy chair and I use the mouse on the chair arm; I can't imagine a more comfortable way to use a computer :) I can't afford 2 computers, I hope to get a good deal on a new one because the one I have keeps crashing. There seems to be something wrong with the inner workings because wiping it clean and starting over didn't help. And anyway, the RAM I have now is truly pitiful.....
Binabik: Depending on your tech availability you could link up a desktop to your TV and use a wireless keyboard and mouse... and hence still sit in your comfy chair.