I've always designed my sites to be about 1000 pixels wide so almost every computer user can see everything across the site in the horizontal direction. What is more interesting is seeing how much of the screen can be seen in the vertical direction.
But you should also consider that not everyone is surfing full screen. Sure, the screen may be 1000 pixel wide, but the browser may only be 500 pixel wide.
For me this doesn’t mean that you should cram everything into something 500 pixel wide or less – sites that are 1000 pixel wide are fine. It’s just that sites shouldn’t break if you shrink the browser window (mind the margins) and the content part of the site (body text, videos, images) shouldn’t be much wider than 500 pixel. All the navigational stuff doesn’t have to be visible all the time, but the site should remain usable. (Since there shouldn’t be many more than 100 or so characters per line, having text no more than 500 pixel wide is certainly appropriate.)
(Luckily horizontal scrolling is a breeze on any current Mac which also happen to be running the OS on which running a browser not full screen is pretty likely.)
Ouch, I hope by about 1000 you actually mean under 974. You're losing another 10% of your audience to gain 26 pixels if you design for 1000.
It's incredible how quickly the userbase drops from 974 to 1050... 10% of users see a horizontal scroll at 974 then it climbs to 50% once you get over 1050... Hope those extra 76 pixels are worth it for anyone designing sites that wide.
