you know, i have my monsterous g5 at the studio. but i got a 14inch ibook and it runs fcp4.5 (havent gotten studio yet) and dvdstudiopro rather nicely.
slower on the render side of things, but heck, i got a g5 for that!
the ibook is great, the screen is nice, and running fcp hasnt been an issue. and its cheaper than a pb.