As for me,
...Some of the best advice I've ever received is to go with the brand that the people around you are using. Group-sourcing lenses and equipment takes the load off.
A perfect example of all this is Otto vs. myself. Given the opportunity, 9 times out of 10 I'll shoot Canon (right now 7d and 5dMkII), but I suspect Otto is the opposite, and would shoot a D800 or D4...
As you suggest, lenses and other equipment are a big factor. You're in a situation where you can group-source such things while I am an individual who has to buy them. I started with Nikon a long time ago with a Nikon F that was pre-through-the-lens-metering. When I could afford to, I added lenses to meet my requirements. I was already doing digital work, scanning my own slides when Nikon first came out with a DSLR, so it wasn't a problem to switch from film to digital. In fact, since I no longer had to buy film and pay for processing, the switch to digital saved me money and time--I didn't have to scan slides any longer and the 14,000+ pictures I took the first year I used a DSLR would have run about $6,000 for film. The side benefit was I learned how to be a photographer because I got instantaneous feedback with a digital camera and I didn't have to worry about wasting film. To make a long story, shorter, I've been using Nikon equipment for nearly 50 years: I'm used to the equipment--feel and operation; I have lenses that won't work on Canon bodies. I'm not saying one choice is better than the other--I don't have experience with Canon; I'm just saying once you make the choice, it generally isn't easy to switch sides. My first Nikon was an accidental acquisition; I accepted the camera in lieu of cash repayment for a personal loan.
And as an aside, Nikon's recent work on ISO is the result of them falling behind Canon in that area. For those reading who aren't that familiar with cameras, there are three things that control the amount of light reaching the sensor (or film): shutter speed, aperture (lens opening or f-stop), and ISO (once called film speed). Faster shutter speed is used to stop action and overcome camera shake but that reduces the amount of light reaching the sensor, which requires either opening up the aperture or using higher ISO. When you open the aperture wider, you reduce the depth-of-field, narrowing the space which is in focus. You can increase the ISO to compensate but as you do that, that amount of noise (especially in ark areas) increases. The other side of this is when there is too much light, you (nowadays, the camera) increase the shutter speed, narrow the aperture, or reduce the ISO. The drawback to reducing the aperture opening is that you increase to DOF, which may not be desirable for the type of photograph you are taking (say a portrait, where you want to keep the background out of focus). In days of film, you had to change the film to change the ISO (you could push the film speed in processing); today it is done electronically. There is also a limitation on how wide you can open the aperture for a given lens, which is one thing that drives up the cost of some lenses.
As a practical example, I have a 80-400mm zoom lens that is rated at f/5.6 aperture at the long end. Nikon also makes a 400mm f/2.8 lens (that costs about fives times as much). If I put the zoom lens on my camera with THE ISO set to 200, the light conditions might be such that the metering system tells me I can only shoot at 1/400 second at f/5.6; however, if I had the expensive version, I could shoot at 1/1600 second at f/5.6. This makes a big difference if you are trying to captrue birds in flight while bouncing around on a boat 20 to 30 miles out in the Gulf of Maine. In some situations, say indoors, you can add your own light.
