I know its cool to see a site automatically adjust by dragging a window, but really you should cater for common screen (full) sizes. AFAIK it jumps from 1024 to 1280 then 1366, so I'd say there's not much between 1024 and 1280 so make sure it looks good on those and don't worry if scrollbars appear on a size in between. Less is generally more in this case, try to just have two variants, three is a max and use stretch width backgrounds etc, so the background still fills the width on larger screens