I'm in two minds about this. I've personally found that when I introduce money into the mix that my interest/passion quickly deteriorates. At the same time, if somebody would really like my photos (be it a racing driver, charity, blog etc) I'm not going to keep them to myself just because I don't want to charge for them.
I intentionally concentrated on seeing how it would go as a 'job' (although around my full-time job as well) for a year and it almost killed my interest in photography completely. I made an awful lot of money and ended up in discussions with sports car manufacturers etc, but sorting the business side of it was soul destroying, and I did notice a subtle 'toning down' of my style to make them more commercially viable...that was the final straw, photography is my passion so my personal view is that I should only ever have to take photos I want to take, not ones I think would make a few quid.
Ironically, my dream was to shoot motorsport trackside for years, but last year I didn't pursue an opportunity offered to me by a racing circuit to be one of their photographers. I do, however, still shoot from public positions and if any photos are good enough I allow them to use the occassional shot for their website / event programmes etc. The buzz from still being able to compete 'with the pros' and have requests for my work from places anyone can shoot far outweighs the financial gain selling photos from positions most people can't access. Maybe I'm odd in that respect, but I've gone one further now and my next goal is to get motorsport shots from Micro 4/3s equipment published, I love a challenge.
So when one of photos is selected for the front page of a heavily visited website or on the cover of a race meeting programme do I feel sorry for the working pros who I've 'taken money from'? Honestly, no. If they were poor photos purposely used for the sake of being free then I would appreciate the issue with that. But they are not going to publish average photos in such heavily viewed places (most are still from pro photographers) so when they use one I know it's because it was the best photo for the job.
I've found a nice balance now, most requests are ignored, but occasionally if somebody takes the time to email me with more than 'can I use your photo?' then I take the time to respond and usually request a copy of the publication for the folder my missus keeps of my published work.