Hoople - 11:15 pm on Dec 1, 2010 (gmt 0)
One factor to also account for is viewport size. This is screen size minus chrome and toolbars. Some users have a boatload of toolbars. Example: Eb*y, Yahoo, Google, Smiley, etc.
I'm on the road now with an older 2007ish laptop, Google Toolbar and have the following screen data: Browser Version: Firefox v3.6, Screen Resolution: 1024 x 768 and Browser Window Size: 1024 x 553