Otakon, a huge anime/nerd convention that books the Baltimore Convention Center every summer and makes navigating the Inner Harbor an amusing, if otherwise impossible, experience. I'm not much for anime, but I went as a favor to a friend and honestly enjoyed myself more than I'd anticipated.
For one thing, the attendees weren't as smelly and pathetic as they're often made out to be, and a lot of them were actually quite nice. There's a real overriding sense of community there that took me by surprise. It shouldn't have, given the shared obsession that guides Otakon (anime/manga/Asian pop culture), but the general mood was very welcoming. People seemed happy to not only be there, but to be sharing the experience with other like-minded nerds.
For another thing, there was a panel on freelancing for RPG companies (meaning tabletop gaming like D&D, White Wolf, etc.), which is something I sniffed around getting involved in until I realized that it's too much work for not enough money or opportunity. But still, some of the panel discussion applied to freelancers in general - the most useful tidbit was that when you're a gun-for-hire, you're writing for whoever signs the checks. Much of this panel was an attempt to dissuade the sperglords in the audience from including 40-page character bios with their submissions to Wizards of the Coast, but the digressions on being an adaptable writer observant of house style/formatting were well taken, and it's good to be reminded that you can be a genius under your own masthead, but not necessarily someone else's.