You might not want to choose this route if you want to use X windows because personally, switching back and forth between desktops is just plain annoying (and last I checked, Seamless mode only works with Windows). Also, if you're going to be testing hardware on linux, you'll probably be better off getting a new machine. But for all other cases, virtualization is the way to go.
My current setup is a Macbook with an Ubuntu 7.10 server VM for development (nothing beats apt).
I got a MBP and immediately threw 4GB RAM into it (~$80 these days! Obviously buy it online and not from Apple). I now run an Ubuntu VM 24/7 that I keep minimized and just ssh into.
Odd, I know, but sometimes the OSX/BSDisms are too much for me. Also, we deploy on Ubuntu so it's a perfect setup for development. Mount your home via Samba if you want to use TextMate or something.