Q: What's the difference between a full-time photographer and a pizza?
A: The pizza can feed a family of four.
But seriously, I have been doing photography professionally for 6 years now. Everyone warned me it would take the joy out of photography. You don't see many full-time pros knocking off work and going and shooting for themselves, but I do. Better yet, I am often shooting for myself when I am shooting for clients. Not always, but often. I love being a photographer, and if anything, doing it professionally has enhanced my joy of it personally, and also driven me to get better, and expand my mind photographically.
However, I barely make enough money to get by. I supplement my income with web design, graphic design, consulting, and tutoring in photography. Little bits of things here and there. For a while I was working in my old job (biochemistry lab) for up to 20 hours per week. It works for me, though, and I'm very happy despite being financially stressed now and then.