You have to allow for all possibilities. Designing a page specifically so that a typical user won't have to scroll means it could look poor on a large screen. I still tend to prefer relative widths, myself, though I know it's a little old-fashioned. And I realise you are more worried about height than width, but I think the old "don't make the user hit the page down key more than once" rule is completely obsolete, and a short page can look dreadful on a large screen. The BBC is a fairly reliable lead to follow: fixed-width at 974 px, you have to use the scroll button twice with a 1024 monitor, and once even on a 24" Mac.