The last Just Cause 2 Multiplayer beta test is set to take place at the end of this week. Starting on December 7 and running until December 14, it's the last time the MP servers will going into beta before the game is launched on Steam for everyone to play (if you can't wait you can get a key here), likely before the end of the year.
We've played through a few lives on the multiplayer servers, and the mod by JC-MP community is a lot of fun. There's sometimes periods of time when you'll not see another player due to the vastness of the map, but when characters do collide it makes for some madcap action.