Robert: The option of running in 2-core or even 1-core mode while under batteries is a very good idea. Somebody tell Apple. I can read/compose e-mail off-line on a long flight on 1-core cycled down to 1 GHz, and do HPC demos at full tilt plugged in when I arrive.
Bizarre article. I use a cluster of Macs to do mathematical work with GridMathematica and the sooner one of these comes out the better - that way I can travel and do demos of parallel computation applications without replying on a local setup. I rarely work off batteries, and the benefits of four processors massively outweigh slightly faster clock speed. Can't wait for quad myself!