I know you don't wanna hear it, but I can't help but warn you about the "tourette's-like" bug that exists with the 15" PowerBooks. It emits loud obscenities about Windows users at random intervals regardless of volume setting. Just thought you should know...
Heh... I would have gone for the same deal. 15" sounds big, but it's actually, as you say, the perfect size for a laptop. I know you'll be satisfied more with the 15" than the 12".