But your site is a computer-based site. Meaning mostly computer-literate users will be going there. and that group of people are the type who are most likely to be using 1024x768.

Really you have to tailor your site to the audience. For instance my GVH site is 1000px wide because the majority of the web users in Gungahlin are yuppie types who mostly have nice new computers that run at 1024x768.

but if you were writing a site targeted at say older-generation people who would (I'm guessing) mostly have older computers they bought in the 90's and thought they'd never need a new one again, you'd want to make it for 800x600..