I have never been and I think it's just generally not my kind of thing in that it's focused a lot around published authors. I'm in fandom for fun and I'm also fairly solidly in the 'don't meet your heroes' school of thought, so the idea of meeting up with writers whose works I loved doesn't really appeal.

It's different for a fan-focused con, where all the attendees are fans and it's more about sharing a mutual love of a canon or a trope or whatever. In those, everyone is more or less on the same playing field (there are BNFs, of course, but they could know your name, too). So I've been to several of those and really enjoyed myself, but I don't think something more pro-focused would be a good fit for me unless I was trying to get into pro-writing myself.