Having given the Pro vs Hobbyist some thought... I think it's better defined by looking at how one aproaches the work rather than simply looking at it as Pro=paid etc...

An amature or 'hobbyist' is probably doing it for fun... and may go weeks or months between works and is more concerned in general with the joy they get in the works they create. A hobbyist can be just as skilled or even more skilled that a 'pro' but isn't aiming at making a living off of it nessessarily.

A pro may be aiming at making a lving off his work... but being paid doesn't make them more or less skilled that the hobbyist (infact I've seen 'pro' works that were horrible compared to some of the work from gifted amatures out there)...

Where the 'pro' differes truely from the hobbyist is in his aproach to the work... he/she daily works on projects in some form, treats it like a job he/she enjoys rather than just looking at it for the fun it can be. The 'pro' also will respond to his end users (clients) in a much more business-like manner where as the amature/hobbyist might not...

In both cases the end result is the same... artworks etc get created, but the major factor between pro and hobbyist is the aproach and attitude towards the work... atleast in my humble opinion...