Realistically the Pro models (Mac Pro and MacBook Pro) should, in my opinion, have optional quad-core. The prosumer models (24" iMac and top of range MacBook) to have decent enough stuff to do the job of a semi-pro and finally the Mini and low-end MacBooks should cater for people after a cheaper Mac.[/qote]
A reasonable assertion, assuming that the change in CPU is a drop-in to an existing motherboard. However, even here we have to tread a bit carefully, as one thing that Apple hasn't done (well, at least not recently) is to build a system that isn't nicely matched. Afterall, system performance is more than just the CPU; one needs to make sure that the other pipes don't get bottlenecked, which ends up with the CPU being strangled for data.
I mention this because one of the things that some cheap PC companies have done is to drop an expensive new CPU onto a cheap old motherboard because they're aware that many PC customers buy based on "what CPU' and then on price. They stop reading specs after the CPU, and that old motherboard is cheap because it has a slower FSB, narrower pipes, etc. The customer ends up with a bottlenecked design that hamstrings the CPU's performance ...but on paper, it looks like it has great specs for bragging rights.
-hh