Please keep in mind that monitor resolution often quoted in statistics is not necessarily the same thing as inner width of browser window. Users may have additional sidebars/toolbars, use non-maximized browser window. The bigger the screen, the less likely you want to use it all just for one page.
Very long lines of text are harder to read. The optimum is 25-30em (depends on many factors, but you shouldn't simply go for maximum).
Mobile browsers have "virtual" screen resolution they use for zoom and it's ~960px in Opera Mini/Mobile and Mobile Safari.
