Dunno really, jan/feb would be my guess if they were…I'm not really sure what the latest is in mobile computer processors but I presume that as the imac has got the latest type of processors (and i think it uses laptop parts) it will be pretty soon that the macbook pro range gets them.
What are you gonig to be using it for? I mean power wise the macbook offers the same as the pro range, but it lacks the better screen, sd card slot, firewire, back lit keyboard and aluminium case.
I'd be sorely tempted by the imacs though, those screens are worth the majority of the cost alone!