If someone has a resolution of 640x480, I'm sorry, but they're beyond hope and they're probably used to horizontal scrolling anyway.

Agreed. I stopped composing-to-640 a while ago.

Still, one should make sure that the page formats correctly on a window that small. Horizontal scrolling is fine as long as the page is still readable and navigable if you do the scrolling. The thing that I don't like to see is a page whose formatting breaks completely at small sizes rather than just making the scroll bars appear. I'd rather have my page render correctly with scroll bars than start wrapping strangely just to help people avoid scrolling.