Excellent hack and works like a dream!
John - given that it already supports 1-on-1 challenges, perhaps a knock-out tournament system could be implemented. Here's what I'm thinking - Set up tournaments with pre-set number of players (e.g. 8, 16 and 32), and also for each round, you could set the number of games to be played to determine the winner (e.g. best of 5 games). Setting up tournaments could also be set in the admin control panel to make it so that only admins can start tournaments to make them more 'official'. Once a tournament has been set up, players click a link to sign up, and once all slots are filled, then it randomly pairs everyone up for the actual tournament.
Too much work? Anyone else up for coding this add-on hack?
The 1-on-1 challenges are great, but nothing beats a proper tournament.