I agree with tjoff; just because a majority of users' screensizes are increasing, doesn't mean we have to keep "upping" the size of our webpages accordingly.

I don't think the guy that just bought a brand-sparkling new 27" cinema display really wants all the websites he visits to now start filling his entire screen -- he bought it to do multiple things at once.

Speaking from experience, I keep all my browsers at around a 1024px viewport and I get frustrated when I visit a site and need to scroll horizontally.

I think the best target size for webpages is still 1024px with 960px^ as its main content area size. The 960px grid is still very strong and useful and there's nothing wrong with it -- I would even go as far as to say that it's a "standard". (http://960.gs).

To me 1024/960 page size is the web's A4/Legal.

^Doesn't have to be 960px obviously...