The festivities run from Friday, August 3rd to Monday, August 6th. If you manage to solve 30 in-game missions during that time, you'll score an in-game t-shirt and 1200 Funcom bonus points for use in TSW's item shop. Free fireworks can also be claimed all weekend (up to 15 per character), and Funcom will be running special event leaderboards to acknowledge the 100 most dedicated mission solvers in The Secret World.
The weekend is also freely available to anyone interested. Whether you have an old beta account, an inactive retail account, or no account at all, you're welcome to take the game for a test drive. If you don't have an existing account, you can sign up for the celebration weekend on the right side of the official website.