Well I have a desktop and I build it to be pretty beastly ( its 2 years old now and still kicks ass at anything ).
specs:
3GHZ Core 2 Quad, 4GB DDR2 ram, hd4870, Audigy 2zs, DFI mobo 1x 320gb - 1x 200gb - 1x 150gb raptor, a dual screen setup( 1lcd and 1crt for color proofing) and z5500d speakers.
I build it like this cause I needed something that could function like a workstation, since I do a lot of 3d/2d work and rendering, this ofcourse had the side effect of it being terrific at everything else aswell, by the time I upgrade this the next "i7" will be out already.
I've also got a laptop, but since I only wanted one to be mobile, I just got a second hand one from a friend for 280€, but the actual laptop was more like 40€, since he also gave me a 9-cell battery, a pretty sweet bag and some other shit.
Overall the laptop is pretty good, but def not meant for gaming, though it manages to play CNC3.
specs:
14.1" screen, 1.8ghz Core 2 Duo
1gb ram ( need to upgrade this badly)
intel gma 350, 200gb hdd, dvd burner
So yeah it keeps me mobile, is able to handle 3d and 2d work, handles 1080p like its nothing and does a tiny bit of gaming.
But if I have to choose, definitly the desktop, build it and love it.