I'm currently in one, and in fact I leave tomorrow to see her for the very first time. We met through last year's PAX; I became good friends with the person I was staying with, and one of his friends was browsing through his Facebook friends and she apparently saw my picture and thought I was "cute". He told me about it, I added her, we've been talking ever since, and are now head over heels in love with each other.
Yes, she is a real girl, I've seen her on webcam.
No, nothing dirty.
Yes, she's amazingly beautiful. The prettiest girl in the world.
Yes, I realize I'm taking a big risk in spending so much money just to go see her. But sometimes, you have to take risks in life to get what you want.
No, you cannot have a picture.
My advice? If you want it and can trust both him and yourself to hold off until you meet (as in, not fool around with other people knowing the other won't find out), then go for it. Save up money and go get him, or have him save up money to come get you. Don't listen to what other people say about it. My coworkers think it's weird, my parents think it's unusual, but my parents at least support my decision. Don't listen to anybody else's doubts if you don't want them to become your own. Is your heart telling you it's the right thing to do? Then it probably is. Hell, it is. No probably about it.
I know for me, things are going to be very, very emotional at the airport when I finally get to touch her for the first time. I get chills* just thinking about it.
Hope it goes well for you!
*Yes, they're multiplyin'.