Finding accurate market share information is next to impossible for global companies. These numbers change wildly between countries.
For example a quick headcount of all photographers I know in Australia would give about 5 Nikons and 30 Canons. One Canon guy joked about how lame it'll be to see all the professional Canon users in the stands during the Chinese Olympics since Nikon was a sponsor. What happened? Not a Canon user in sight. Every Asian tourist I saw in Europe had a Nikon, everyone (not tourist) I know from Austria is split evenly.
Then there's nothing to be trusted about what manufacturers claim either. Canon claimed a while ago how absolutely massive their 1D Market was, except they double dipped the numbers, and all those that came back with focusing problems were counted as additional sales. This isn't anti Canon, I am sure Nikon is guilty of the same.
Most importantly the market share is almost a seasonal change. When the D700 was released Canon sales took a massive hit thanks to all the hype. There would have been many photographers who jumped ship because of Canon's low light performance at the time. Now it seems every second person is uttering the words 5D MkII, and I'm sure many Nikonians are jumping ship disgruntled that they can't get a +16mpx camera for under $5000.