Actually, depending on what you're doing, the Nikon AF system is occasionally better than the Canon system. And occasionally also at least as good. A colleague whom I trust and respect immensely recently did the Nikon to Canon switch under pressure from clients, and his feelings are that the AF is more or less the same. He still has his D2x for a variety of reasons including preference for personal shooting. I've been in numerous situations where a sequence of frames will be similarly out of focus with both Nikon and Canon cameras - the basis of both systems is probably remarkably similar; and what messes up one system similarly gives another problems.
As for the percentage of sports photographers; I'm not intimately acquainted with the US state of affairs aside from understanding that they are even more Canon than us in the UK. In the UK I would say that 80% might maybe be a very conservative number; the proportion might be closer to 90%. Amongst the news photographers that do some sport, there is still a good number that still use Nikon, but amongst the dedicated sports snappers there are very few that remain.
That said, the D3 is making waves already despite not being available commercially yet. Snappers who have been to Osaka are impressed (Canon users), and back home in the UK for example Dan Chung was writing that he was impressed enough to have a couple on order; and he's been Canon for ages. Balance all this with the fact that that Mk III is having problems (took it out of the box, tried it out, it's been in the box for the last four weeks being one response I got), and who knows.
Too many agencies and photographers have a LOT invested in Canon for there to be a monumental change in the industry, so I doubt a lot will happen in the short term. What it does mean is that for someone like me as a Nikon user, I can now compete on a level footing when the days get shorter and we have to shoot under (usually dismal) lights.
