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As much as I joke to my friends about the rivalry, I think I'm actually pretty agnostic.
I think a good approach, like you are thinking, is to look at the lens classes you want to buy, and compare how Nikon and Canon will cover them. There are some key differences that could sway you one way or another. It's also important how the camera feels in the hand, although first impressions can be deceiving, and you have to compare comparable cameras.
17-55/17-55 differences: Nikon's 17-50 f2.8 is a pricey ($1100'ish) lens. It's more a more solid build, and at least reputedly sharper than Canon's 17-55 2.8. *BUT*, Canon's lens has IS while Nikon's does not. I myself consider IS very important in zooms. However, if you're shooting action, you want to keep shutter speeds up anyways, so IS is less important.
fast telephoto zooms: Nikon has an 80-200 (non-VR) 2.8, and two versions of the 70-200 2.8's (VRI and VRII). The 80-200 is kind of for people on a budget, since it's $100 and doesn't have VR. There's also the 70-300 f/4.5-5.6 VR. Out of all these, the 70-200 2.8 VRII I think is the clear leader here, but it'll eat up a huge chunk of that budget.
The crop telephoto zooms (Sigma 50-150 2.8, Tokina 50-135 2.8) are good budget options, but none of them have IS/VR/OS, etc. Sigma may come out with an OS 50-150 2.8, but we've been waiting for it for 9 months now with no announcements.
There is a big differentiation with other lenses: Nikon's 35mm 1.8G, at $200, is a very compelling option for a Nikon starter. It's roughly a 50mm equivalent. Canon's 35 f/2 is like $350, and the Sigma 30 f/1.4 is $350 or more. But there's also issues: All Canon bodies can autofocus their 85 1.8, 135 2, etc. Nikon's cheaper bodies (D3100, D5100) cannot autofocus Nikon's 85 1.8. Since your friend seems to be very interested in a lens platform, it's generally recommended that he goes no lower than a D90, and opt for a D7000 if he can swing the bill ($1200).