I got to attend the first and only Flanvention a couple of years ago. The second one was cancelled abruptly, and all sorts of bad surrounded it. I don't know what happened there, so I can't speak to it. (Many of the cast, including Nathan Fillion, showed up to the bar at the hotel where the Flan was supposed to be, and I think that's just six kinds 
of cool.) The first one, though, was fun. I met a lot of great people there, professional and fan alike.
One of them was Brenda, the photographer. She remembered me, and got in touch with me to have me do a caricature of Joss Whedon as part of a "get Joss Whedon a star on the Hollywood Walk of Fame" project. I'd done caricatures both live at the event and of the cast for the program book and she liked my work.
I had to guess at his eye color, but other than that I think it turned out swell. You can find out more about Brenda and her campaign for Joss here.