I guess having 8 processors (2 AMD quad when they come out) would eliminate lag maybe? I dunno how often 8 is gonna be better than 4 though.
Depends on the software in question, but increasingly you're going to see applications get better at taking advantage of multi-core architectures. For example, the application I'm currently working on scales well to dual, quad, etc core systems.
I suspect one quad would be ignored in Windows Home, but I don't know much about it.
No, XP Home would recognize all four cores, so long as it was a single physical processor. On the other hand, if you had two physical processors, each with a single core, XP Home would recognize only a single processor.
As is, I'm saving up for a big ole, top notch intel quad. Maybe I'll get at the end of the year (I want to get something good). Hopefully DFI will have a new board (newer than ICFX3200-T2R/G) out by then.
I'd really like a dual or quad core system; my next build will definitely be at least dual, although by the time I actually build something, we'll probably have 32 core processors or something ridiculous like that...
(I have ridiculous buyer's remorse, can never purchase anything. It's terrible)