It's one of the dumber design aspects of MediaWiki and Wikipedia and their skins that the site fills 100% of the screen width, regardless of resolution, leading to a ridiculous appearance on high resolution monitors.
Short of a grid layout or other sophisticated approaches, what is required is a sensible max-width for the entire site layout, in the order of 1000 - 1300 px I suggest, allowing the site to scale horizontally below that but freeze on decent res screens.
I had a bunch of CSS modifications for Monobook that worked well, but they made use of the #globalWrapper which is not present in Vector. I am trying to migrate my old Monobook styling across to Vector.
I played around with adding styles to the various page elements in Vector, and even the <body> tag, but ended up frustrated trying to get the header and sidebar elements to cooperate.
Has anyone worked out some CSS for Vector that does the trick?