A few days ago, the designer working on our sites asked me stats about the browsers visiting the sites. She already had the general data available, but this time what she wanted was the info about the "other" browsers.
Which is quite true: once a site has been designed to standards and the quirks of the two or three major choices, work has to be spent on the non-standard non-mainstream ones. But to what extent ? Here are the data.
First, a general graph of all browsers met on the sites since 2000. Of course, MSIE6 masks most recent evolutions. Notice the small NN4 hump in late 2005: since it has no reason to be strictly a local accident, as these sites attract thousands of visitors daily, my idea about it is that it is a direct consequence of the Firefox buzz: Mozilla/Netscape becoming fashionable, causing users to use the original Netscape browsers again, before concluding on its uselessness these days and returning to a more current browser. (click on either image to see it full size).
Now, see what happens with MSIE6 and Firefox are removed from the overall picture. 
I left MSIE5 in this chart because it is slowly becoming irrelevant. the NN4 accident in late 2005 becomes more striking, and suddenly other information becomes apparent: while the minority browsers like Safari / Konqueror or Opera seemed statically insignificant, they now appear to be growing within the overall "alternate browser" ecosystem, at the expense of older browsers, if not at the expense of the current 200 pound gorillas.