One of my good friends who is a professional wildlife photographer, uses his flickr to get his work out there, and has ended up with his work being selected for a few magazines just from his flickr account. If you do it right, it works great for wildlife photographers. Being an assistant is a great start, especially if you do not have any formal training, or want to get your foot in the door somewhere. I never denied that. But again, wildlife photographers are a different kind of beast.

Also - Cropsis is bad. Having a cropped sensor can be bad. But I know plenty of professionals in their field that use a Canon 7D over a 1D Mk IV or a 5D Mkiii full frame cameras, because the sensor is just fantastic and the crop gives us that extra bit of reach when we need it.