This all sounds pretty interesting, and good news for people looking for iBooks. But (and I've said this before) the low-cost laptops can still converge with their higher priced bretheren in terms of form factor and design. They will more than be able to differentiate the powerbook line with multi-core CPUs, replacable graphics cards, etc.
My prediction has been for quite a while that the lower-cost iBook will converge with the more upscale powerbook in form (widescreen, etc). You may see the iBooks go Aluminum while the PBs go with some other material, so there will be just enough of a cosmetic difference to make the PB purchasers feel like they got something "more". But I figure that we'll see a 13.3" widescreen iBook as well a 13.3" widescreen PB. If I'm right, the 12" PB may have seen it's last days.
I wonder how the "pro" users that like the smaller form factor would feel about that?