I have seen such stats recently! But I can't remember where. The break down was that most users were either Firefox 3.6/4 on Windows or Chrome on Windows, followed by Safari or Firefox on Mac, followed by IE7/8, followed by Firefox/Chrome on Linux, followed by other. In a very approximate way. Basically, the takeaway is that an unusualy high percentage of our users use either Firefox or Chrome, and that there's almost no (not zero, but close) IE6 use. (This is probably in large part because the official site portions do not support IE6, and display funkily in it.)