A constrained liquid/elastic hybrid is what I’ve found works best for most content-rich sites. A navigation column and/or sidebar that is elastic (”fixed” width specified in em) plus a liquid main content column. Then you assign a max-width to curb the problems with overly long lines of text, and perhaps a min-width to prevent the content column from collapsing in extremely narrow viewports.

The min-width and max-width properties aren’t supported in IE6 and older, but this behaviour can degrade gracefully. Specify an em-based width in an IE style sheet, and use Microsoft’s proprietary expression() syntax to emulate min-width and max-width for the majority that has client-side scripting enabled.

Of course there are sites that will work best with a rigid fixed-width layout and sites that will work best in a pure liquid layout, but those are quite rare.

You can use min-width with divs, p tags etc and while it does not work in IE (you can use a hack) it does mean you do not have to read a sentence over 1200px.