My opinion:
WWDC stands for "Worldwide Developer Conference" that is the most suited place for "pro apps" related information as well as OS related ones. Of course iPhone is the Steve's creature and it will have a prominent space.
The way I see it is the following:
- announce iPhone 3G
- peak at 10.6 which will be the last OSX iteration. Next one will be OS XI (with a more prominent space theme (and name scheme)).
- Maybe also some info about pro Apps (Aperture, Final Cut, and the like)
New MacBooks and MacBook Pros (as well as, possibily, new MacMini and Mac Pro, including cinema display (LED cough cough, a lot thinner...)) will be announced towards the end of the back to school program (or right after it) at an invitation special event. This also because Intel announced delay in shipping Centrino 2 platform. This allows Apple to concentrate on Developer related issues at WWDC.
Since Jobs is no "developer" himself, his keynote will be centered on the "fun and ooooh" stuff like, as I said, 10.6 and iPhone. With the announcement that 10.6 is the last OSX.
OS XI will mark a clear cut with the "old" tech (Carbon, 32 bit, PPC support among others, possibly old file system as well). 10.6 will introduce option for ZFS but OS XI will be ZFS only. So transition will be made smoothly with the last to releases of OSX (Leopard and the next one). And then a fresh new start with OS XI (just before Windows 7 SHOULD (stress should) be made available).