Some might also not use the full width of their screen. Is there any good data on this?
My browser window is nearly always about 700px wide – that’s half of my screen. Two-finger scrolling makes vertical scrollbars just as easy to use as horizontal scrollbars but 1000px wide designs are not optimized for 700px wide windows [+].
I certainly don‘t want websites to start using 700px wide layouts. I would, however, love to see more websites that change their layouts depending on the width of the browser. Twitter could drop one column if needed. Many browsers already make such changes easy and it is just as easy to force the common denominator layout on older browsers. That would be completely in line with progressive enhancement.
[+] To all the web designers out there: I can understand that it is not exactly your priority to make it easy for someone who like 700px wide browser windows to use the website you are designing. But could you please at least test whether everything still works even when the browser window is that narrow? I really should always be able to scroll to any button and backgrounds shouldn’t disappear.
Seriously? 700px? I realize there's a class of users that doesn't browse full-screen, and that a site with a broad an audience as Twitter is bound to encounter every variety of screen resolutions, but there comes a point where if a user elects to operate their system in a non-standard configuration they can't expect the designer to accommodate those requirements when there's already two solutions available to accommodate this choice: scrollbars and the zoom-out feature available in every browser.
While developing alternative display modes for non-standard resolutions is certainly possible, it unquestionably increases the time and expense of design, development and testing for what is arguably a negligible gains in terms of the percentage of users you're serving.
I understand that it is additional work and I really don't want to be demanding. I’m happy when a website merely works. (I’m not sure how non-standard windows not spanning the entire width of the screen are. That seems like the default behavior of any browser window on the Mac. I would love to see data.)
It‘s just that many, many websites are being optimized for low resolutions on mobile devices anyway. It would be great if that work could be repurposed for the desktop.