Systems: Lion. Ubuntu 11.04 through VirtualBox (for patch contribution). Windows 7 via Boot Camp (for Deus Ex and Fallout 2). Used TextMate for a while, now I'm back to Emacs in Terminal.
There are some obvious drawbacks (glossy screen, poor GPU) but I dig the mix of portability and expandability lacking in both a MBA and a 15" MBP.
What do you develop for? Are your tasks memory- or CPU-intensive? How often do you work away from home? Do you prefer to replace your computer often, or do you run your laptops into the ground? I ran my last Macbook into the ground (and use it as a media server now), and I expect to do the same for this MBP.
For what its worth, if I wanted to roll my own Linux laptop I would've bought a Lenovo. I hear they're engineered very well and weigh almost nothing.
It's not what you own, it's what you make of it.
desktop at home: 27in iMac
on the go: 11in Macbook Air