You always have to take into consideration the average user, not your resolution. Maybe you can work on a 30′ Apple Cinema display, but others not. 
And if the site looks good in 800×600 than the users up to this resolution can read it well, too. People hate horizontal scrolling.
(This is the same that you can work on a T1 but a lot of ppl use dial-up, and you don’t want to lose them as a potential player just because your site uses heavy images to download, do you? 
)
You can find here resolution and other statistics:
http://www.w3schools.com/browsers/browsers_stats.asp