Think Secret is confirming that new iBooks are coming tomorrow and adds some information of unconfirmed sources :

One unconfirmed tipster has since said the new iBook will feature G4 processor speeds of up to 1.3GHz, while another has said the laptop will sport a white latch instead of silver to differentiate it from predecessors.

The processor speed is also what our sources had expected. Think Secret is not confirming the price drop mentioned by MacGadget which was the first to talk about iBook updates for Tuesday.