Ars Technica reports the world market shares of browsers in 2010.
As a personal observation, my days of loyalty to a single browser are over. I use Firefox a lot of the time, and Chrome increasingly with Google sites including YouTube and Gmail, because it just loads so much quicker. I notice that with flash-heavy content, Firefox hogs a huge amount of system memory. This is not the case with either IE or Chrome.
The only loser in this is Opera. I remember the early days Opera came out (the days of Dial-up internet) how good I thought it was. It's a pity its not been able to keep up share and keep up a user base. But let's see how it does now, with the mobile platform also being available for browsers.