Thomas Baekdal has done a comprehensive analysis of actual content usage space in a browser, coming to the following conclusion:

Finally we can see what sizes we need to design for. E.g. if you want to design for 95% of your visitors you need design for no more than 776×424px (fixed layout) - or between 720×400px to 1408×912px (fluid layouts). You can also see the pixel “gab” when designing fluid layouts - at 95% it is a staggering 688px in width and 512px in height.

This report reminds me somewhat of my search engine vertical space test. Too often web designers don’t give the content enough room to breathe. Perhaps I’m in a small minority but I’d rather see a site go members-only and stay easy to consume the content than remain ad-supported and a mess of tangled ads with content. How many good content sites can you think of that have ruined themselves by drowning the content with ads? Some sites start out with too many ads, thus severely limiting their chances for being linked and bookmarked by others.

While on the subject, here’s a good list of 250+ webmaster related tools.