Lenses from Nikon

Recently I've been researching Nikon lenses. I'm a Canon user, but some of my friends always try to persuade me to check out Nikon. I don't think I will, but must admit they do have some good stuff. I mean once you're chosen your brand it's rather hard to change (not that I really want to!). But say I did want to chnage to Nikon, I'd have to sell all of my Canon gear and buy everything from a scratch. That's why it's so important for those companies to attract beginner photographers and automatically make them loyal customers.