Despite Microsoft rushing IE 9 out in beta to capture some additional market share it looks as if IE is still on the decline. Data from StatCounter reveals that IE only has 49.87% of the market - that's around 50% to most numerate techies. Firefox has around 31% with 12% using Chrome.
Given that IE's market share was 67% just two years ago this looks like a real change. Of course you have to take into account the fact that there is more choice now. It is a standard marketing technique to introduce new brands simply to reduce your opponent's market share - even though there is no suggestion that the introduction of new browsers is orchestrated, additional choices reduce everyone's share.
Another interesting factor is inertia. Users who find IE on their machines tend not to bother to change even though the alternatives are free. In Europe Microsoft has been forced to give Windows users an initial choice of browser and indeed IE use has dropped to around 40%.
Microsoft's attempts to increase its market share by releasing IE 9 beta might not be working as well as they might for the simple reason that it doesn't run on XP. Recent data indicates that 50% of Windows users are still running XP and hence can't upgrade to IE9, not so with Chrome and FireFox. If things continue in this way Microsoft may have to think again and release a version that does work on XP.