I didn't; I bought a BlackBook. Here's why.
I'm as much of a Pro user as anyone can get, but I cannot stand the aluminum enclosures.
As someone who administers a whole slew of Macs, I can tell you I've stopped buying Apple's aluminum laptops unless the user practically forces me to. Almost every aluminum PowerBook and MBP we have is bashed in in some way or another. Usually it's a corner(s) that is caved in, but sometimes it's the DVD slot, other times the area around the DVI port. On some, it's all of the above.
Even my careful users' aluminum 'books become dented after a couple years. And the dents aren't just cosmetic. A dent by the battery means the battery isn't properly seated. Dent by the DVI port means it is difficult/impossible to plug in ext. video. Dent on the optical drive can make the drive unusable. And so on.
With the iBooks and MacBooks I have never had any issues with the case.
All of that said... I really wish my BlackBook had a better graphics engine. I can definitely notice the chipset-based graphics. (Though maxing it up to 2GB of RAM is a definite improvement.) Nonetheless, it is a price I'm willing to pay to not have to deal with that aluminum. No way am I doing that to myself.