>>ergophobe, have you designed any sites that are broadsheets ( >1024 ) yet?
Not yet and I don't think I'll ever do a fixed-width design that defaults larger. Basically, if you go beyond 35em (about 60-70 chars) readability declines. I know that's nothing you don't know since that issue is implied by your first post.
That being so, with normal sized fonts, the main text area can only get so big. So any wider layout seems to me to work only with
- text columns, which will work well when CSS3 is more widely supported
- additional columns of ads and other "noise" that in effect only gets displayed to users with wide screens.
And then with the issues that ken_b mentions, plus the mobile issues I mentioned, it seems like you need a minimum of four layouts, perhaps five.
380px for mobile
740px for "narrow"
960px for "standard" display
and then a wide and a super-wide
Doing something along these lines has been on the TODO list for a site that I think might attract a more mobile users if the layout was more friendly to them, but alas the site pays its own hosting bills and not a lot more, so I just haven't found the time to put into it.
Did you look up any of the articles on Switchy McLayout? That always seemed to me to be the right general approach.