There are plenty of statistics available on screen sizes/resolutions and their usage. Equally there are plenty of articles available on how you should optimise your site design for this size or that size.
The truth is that screen resolution is only half of the equation. The other half, and more important for the end-user experience, is the browser viewport (window size).
A user might have the world’s largest screen; but unless their run their browser full-screen, this fact isn’t very relevant to us. And even if they did; they might have so many toolbars, bookmarks, and a page history sidebar that their viewpoint will only be a tiny fraction of what you might expect.
We need to switch our focus from screen resolutions. Web usage is diverging; for some screen sizes are getting bigger. Whilst for other screen sizes are getting smaller. Website statistics suites need to gather data on visitor’s actual viewports – it is already possible in some – so we can move forward.
In October 2009 an interesting project began. w3census intends to help developers, with a live database, to be always up-to-date with the current state state of the web. In that database will be, amongst many other things, Browser Viewport Size. One to watch.
Update Jan 2010: w3census has vanished, including their twitter account. Shame, it looked interesting. In the meantime, I’ve added written a post explaining how you can measure browser viewport size yourself.