I know what you mean about the Powerbooks -- I used my brother's G4 Titanium when visiting him last month and fell completely in love. A huge compliment as I've always been a vigorous hater of Mac OS's.

The single mouse button isn't a problem if you get a Wacom Graphire2 or something similar. It comes with a two button +scrollwheel mouse and costs a hundred bucks. Not a studio grade tablet, but definitely up to the task for your average power user.

I can't believe I'm helping someone decide on a Mac...