I haven't gone to a proper convention yet, but I have been to the Student Roleplaying and Wargaming Nationals several times, and they have stalls at those events. When I went this year, I picked up a copy of Night's Black Agents and it's easily the best RPG I've bought at a Nationals since I started going. I was a little dubious about the genre mix of spies and vampires at first, but having read the book I can't wait for an opportunity to play. And I do mean play. I'm happy enough to run it, but I really, really want to play as a character.
I'm a big fan of the Gumshoe system in general - even though I haven't quite got the hang of running it as a GM - and Night's Black Agents is second only to Ashen Stars on my want-to-play list from the Gumshoe family of games.