Super-telephoto Lenses

I don't have a DSLR camera yet, so I have no need for a super-telephoto lens at this point in time, but the advise given by Tim Fitzharris in his book "Nature Photography" proved to be very helpful. I don't know a whole lot about photography equipment, I just use my little point and click Nikon camera right now. I like to research things before I buy them, so all the advice I can get is helpful. I like his statement that if you're restless, not terribly big and like to get off the beaten path, then the 500mm is your focal length. This is good advice from an expert on the 500mm vs 600mm debate. Although, I am a long way away from purchasing a super-telephoto lens it is good to have this kind of input. I prefer to go off the beaten path and, while I'm not a sissy, I am also not the biggest bloke around, so the smaller lens will suit my amateur ambitions just fine. He has me sold on Canon lenses for their diffractive optical elements that eliminate chromatic aberrations and reduces the size and weight of the lenses by three-quarters and two-thirds respectively, now I just need to increase the size of my salary so I can afford one. Also, being one of the two companies that have image stabilization in their super-telephoto lenses makes Canon even more desirable. I don't pretend to understand all the technical advice he gives, but I guess I'll figure that out when I get new equipment that utilizes everything he is talking about.