An awful lot of talk about Reuters in this thread. There are a lot more agencies than just them, and then there are those photographers commissioned by newspapers and such. I attend a lot of media events, including sporting and the boring conferences etc and generally I would say I see more Canon. BUT, in recent times Nikon has been growing quite rapidly in numbers and I know a few (freelancers) that have switched from Canon to Nikon. To be very honest I do not pay that much attention. I think a lot of people here would be surprised at how old some of the kit is. There are people on this forum with much more advanced kit (and much more of it) than many of the pro photographers that I know and see on a regular basis.