Regardless of screen size, it is still prudent to hold the width of your main content to under 800 pixels, and some might even suggest as narrow as 600 pixels, which still nicely fits two columns of text. This closely matches a sheet of ordinary A5 paper (~8-1/2 x 11) with margins.

Every user has different preferences though we may be hard pressed to find any that have a fondness for the horizontal scroll bar. Fluid layout helps to some degree, as long as the developer places constraints on the main content size so that it doesn't slip off the screen for narrow width viewers. What some sites do to help curtail the horizontal scroll is to use javascript to collapse outlying content.

We should not assume that one size fits all when it comes to choosing whether to go with fluid or fixed. It really does boil down to intended audience and the purpose of the content. If your audience is largely made up of 'dinosaurs and troglodytes' then their special needs will be a major consideration. Fixed width still does have a place in the scheme of things, albeit perhaps a thin sliver in terms of the global pie.

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