OnlineDM
Adventurer
Litmus test: Do you make enough money in game design to have to legally claim it on your income tax (whether you actually do or not)? If yes, you're a professional. If no, keep going. Do you earn enough money per month on average to buy at least a single used video game? If yes, you're probably an amateur. If no, you're probably a homebrew.
Interesting. I see this very differently. Maybe I'm too literal on the definition of "amateur" but I understand it to me someone who does something solely for the love of it rather than for money.
So, Matt James and Mike Shea would both be professionals in my book. I'm an amateur - I've released four adventures on my blog for free, but I've at least put them together and put them out there. Had I just written those adventures for my own game and never shared them with anyone, I'd be a homebrewer.
I'm sure there could be some fine distinctions made: "Oh, I once got fifty bucks ten years ago for an article in an RPG magazine..." would probably be an amateur in my book since they're not doing it for money any more, but if that guy wanted to call himself a pro I wouldn't fight him.
In any case, the poll is asking us to self-identify, so there's no right or wrong definition here. It's whatever you call yourself.