I found this interesting pie chart showing reflex cameras market share in Japan during 2007:
Nikon and Canon are more or less the same, and together they have more than 80% of the market. I did not found data for Europe or the USA, but I guess Canon and Sony have much more market share outside of Japan. Dominance of Canon and Nikon is nothing new, what is noticeable here in Japan is that Olympus and Pentax are starting to take off.
Right now I have a reflex Nikon, a compact Canon, and a Fujifilm super-zoom. I love them all, each brand has his way to organize menus, limitations, advantages etc. And that’s good because you learn a lot from one camera’s limitations and the other one advantages and the other way around.