I certainly think it's worth waiting for Rev. B ...
-8x Superdrives (I believe they now have 8x superdrives of the same measurement requirements that the powerbooks use)
-FW 800 (although FW is loosing ground to USB 2.0, it'd be nice for legacy item support)
-More USB 2.0 bays (many PC laptops have at least 4, many PB's only have 2 if your lucky)
-Lithium Ion batterys (why didn't you use them Apple?!)
-Intel counted at least 40 bugs in the Intel Core Duo Yonah CPUs.
-Better video card option (Apple has never offered good video cards on any other computer but the insane powermac)
-Good BIOS and EFI support
I know I certainly won't be buying one of these until Apple covers at least 3/4 of these things.