Apple lowered the price on the powerbooks in early june to clear inventory (or so the story goes). The new PowerPC 7457 based 'books were supposed to come out in late June. Since then the rumor has been "Any Day Now". Apparently Motorola are completely unable to supply the darn things, because now the story is that they won't come out until October.
That's almost a year after the last update of the 15", and ... well, also almost a year after the 12" and the 17" came out. And the retain channel and the distributors are almost completely out of stock.
Unless they have a contract that makes this hurt for Motorola, then Apple is in a really bad spot.
Apple: "Make the darn things already or we'll change chip supplier!"
Motorola: "Er, you already did."
Apple: "uuuh... Because you suck!"
Of couse, maybe this will make G5 powerbooks and iMacs come out sooner... (the G3 in the iBooks is produced by IBM).