Its better to use a program like HLSW or Xfire to join the servers outside the game, especially if you have a reserved slot. Valve's server browser refuses to force connect to a server that is full. That and if you don't have the game running you have a small chance of a slot freeing by the time the game loads and tries to connect. That along with Steam's bad history of randomly clearing your server favorites/history/filters. There are a ton of "server browsers" out there. HLSW is really great and supports a lot of different games and can be configured to support third party mods.