Just a quick note, today. My personal way of working is close to some kind of multitasking. As I personally have only one processor (“the brain”), things do come out sequentially, but I am quite convinced, that the brain actually operates many parallel threads at the same time. Of course, most of this are independent, autonomous processes connected with the bodily functions etc., but some threads are obviously some kind of sub-conscious analytical processes, to which the consicous mind passes pressing problems to be processed without any external disturbances. Then at some point, when your conscious level of the brain has reached a point in its progress, to which these sub-conscious processes have some relevance, they send an interrupt and require attention.
Practically, what this means, is that the ideas, what to do with the data often appear in the middle of the writing process itself, and force me to divert my attention from producing as much text as possible to performing some new analysis with the data. Now, with the traditional, single core systems this used to mean a halt in the writing. No matter how nice you tell your GRASS module to be, it still seems to bog down the system while doing something with your ~30M cell raster. Now, with the modern nay dual-core processors, this does not happen any more — the GRASS module takes everything the second core has to offer, while I can still keep happily using the first one to all the other things.
Especially nice this is on my work computer, as I run GRASS on Debian as a VirtualBox virtual machine. VirtualBox occupies the second core completely, while the rest is left to the actual OS (XP, in my case) to run my Emacs and other stuff. Probably with Quad-core I would feel like wasting the cores, but for my purposes, a Dual core system is very nice indeed.