So we've started a Diplomacy game (
http://www.webdiplomacy.net/board.php?gameID=80849 ). Diplomacy is
a game with extremely simple rules, where winning the game is based
more-or-less entirely on your ability to negotiate with the other
players (and then betray them at the best time :D).
I think this is a very good format for demonstrating proficiency, in
a manner similar to my commentary earlier about "if you can figure
out co-operative puzzles, you are competent". I imagine that
whether or not you can win at diplomacy with turns of a given length
says quite a bit about your proficiency with Lojban. Turns of, say,
two minutes long would push your Lojban ability to the limit, I
imagine.
-Robin