Here is the browser market share for June 2008, based on traffic to my top site:
Firefox 3 was released in the middle of June, and it did not have much impact on the browser share for June. In fact, none of the browsers moved more than 0.1% in either direction. This was slightly surprising to me initially as I expected Firefox to gain some market share given all the buzz around Firefox 3. However, going through the data, it appeared that a fairly significant amount of people had already been using Firefox 3 prior to its official release, so the release itself did not generate much additional usage.