At PAX Prime 2010 ArenaNet hosted a panel that let Guild Wars fans come in and help design an entire event chain in Guild Wars 2. It starts off by selecting fans who were actually interested and invested in the game and sticking a small group of them in a panel. Then they explained what the dynamic events system was and gave everyone a choice of three regions that they could design an event in. Timberland Falls was chosen and from there an entire event was designed.
After an hour and a half of discussion, the designers and audience had created and diagrammed an entire storyline that revolved around saving the quaggan from the krait. The event chain combined assaults on krait structures, recruiting nearby allies, forging an undersea super-weapon, hulked-out quaggan, a boss creature known (for now) as Mega Uber Shark, and much more.
This is perhaps the coolest swag you could ever get from a con. Think about it. You show up and then all of a sudden you're helping design the game yourself. Anyway, you can view more details at the ArenaNet blog.