I'll probably eventually upgrade when Apple release a 12" MacBook Pro.
They won't be. As far as Apple are concerned, the 13.3" MacBook, 15 and 17" MacBook Pros are the complete line up. No more 12"...
Since Apple's move to Intel there'll be a lot less PPC-based machines around to run linux on, so it may not be worthwhile to go to the effort of making a linux ppc Max... unfortunately.
Of course... Cell would be a different matter entirely :-)