The problem with the new Imac has to be a heat problem, more then they have expected. How would Apple get sooo much heat out of such a small box and still keep it silent? They will have to make some sort of fluid cooling system. There was an article/rumor a while back that Apple was talking with some company that had developed a new kind of liquid cooling system, and I am not talking about the one in the new PM! This one could be built in laptops. The fluid wasn't waterbased, but something new, more like a paste. Don't know the exact things anymore.
Anyway, IBM has a problem with producing enough fast cpu's, therefore the "rejects" will run at a lower clockspeeds. So there are probably enough chips, so it has to be a heatproblem! The same was with the Xserve (why isn't that one clocked any higher then 2.0? That model can make noise!!) and with the new PM's. Think about it and add up all the previous rumors, it all makes sense. My prediction is an entry model with a G5 1.4, the mid a 1.6 and the high end 1.8. In that way there is also enough speed difference between a PM and an iMac.