If I were you I'd wait for the G5 Powerbooks.
They aren't too far off... and once you get one, the time between upgrading to your next will lengthen dramatically as the platform is substantially better.

I got dicked buying a powerbook too late into it's lifecycle, and then a month later when the new ones came out, the lowest end one was better than my high-end one, and $1300 cheaper.

Ouch.

Just my $0.02 ;)