I'm not sure that I understand the comment about crop sensor cameras being for amateurs only. There are tons of benefits to having them. They are typically faster (great for sports) & they have a much higher pixel density (great for cropping). Both of those are reasons enough to be a number one choice in many situations.
Don't get me wrong, I want a full frame, but even with one I wouldn't always use it. If I were taking pictures at a game I would definitely choose the crop sensor, and if I were shooting wildlife I would probably go crop sensor also. What's the big advantage with having a full frame? More picture? You can get just as much picture with a crop sensor - just take a couple steps back. Now you have a higher resolution image of basically the same thing. Also, don't full frame cameras have issues with the edge of the picture sometimes? They are also typical worse at handling noise right?
Either way, I'm curious to hear the reasons why FF cameras are pro cameras and everything else is for amateurs. By that logic the 1D is basically a Rebel.
Full frame cameras can be prone to vignetting and unsharp corners in poor quality lenses but they make the most a camera can out of an EF lens. Why waste glass and only use the middle of it when you can use it all? The focal length change gives an apparent shallower depth of field as you can then get closer to your subject also. I would hate if my 50mm wasn't actually 50mm...
Another massive reason for full frame is its hands down superior noise handling. No crop sensor compares and noise reduction technologies don't count as they affect the sharpness of your image.
They both have their uses.