If I was apple, I would announce new Macbooks 2-3 weeks before Leopard ships, saying they will ship with Leopard. It would eliminate the drop in sales they have to be expecting in the weeks prior to Leopard. And, they can also get two news hits out of it. "Apple announces new Macbooks, will ship in 2 weeks with their new OS code named Leopard" and "Apple releases new OS, it comes pre-installed on all new computers, like the new Macbook which was just updated 2 weeks ago, and is shipping now."
As for what the update will be, I'm thinking a case redesign. Aluminum but rounder edges than the MBP, more along the line of the nano.
I see it breaking down as:
Base model: Sliver only
Middle model: Silver and colors
Top model: Only black
Like the nanos were until the last update.
As for tech specs:
Upped to Santa Rosa (which means at least GMA 3100), maybe LED, base RAM in one Dimm, maybe an extra USB port on the right side, Standard super drive (make the speed the difference between base and middle/top models)
Anywho, those are my predictions (slightly inspired by my iBook's logicboard failure)
~Thursday