The iBook does not ship with a G4, it comes with a 500Nhz G3 that does not have a velovity engine. Other than that it is a kick-ass machine (given that you can up the ram to 256, a combo drive, built in airport, USB, firewire, modem, ethernbet, RGB, speakers, 1024*786, 20Gb HD and all those for about $2100!!! ... I waaaannnttt ooonnneeeeee)
Actually the new iBook is the same as the old one except for the faster processor, extra USB, combo drive, and higher resolution screen. I would NOT sell my G4 for an iBook. I am planning on selling some older computers to get one to go with my G$.