I'd take the powerbook. When I get from work, all I want to do is take off my pants and trade them for shorts... byebye shoes and socks.... hello ibook, lets head-on to the hammock, bed, or sofa.
In the past, whenever Apple released a new iMac I wanted it badly! Now that I've had an iBook for about two months, I only see it replaced by another portable. An iMac with a 17 inch screen?! Eh...