Betfair have started a new section of their site - Betfair Taikai.
They don't seem to be advertising it yet, so there aren't thousands of users yet.
I've been playing for a few weeks and have been doing quite well.

The tournaments are a bit like 'tipster' challenges where you make a series of predictions on outcomes of sporting events and pit your skills against other people.
There are free tournaments and 'buy-in' tournaments for £5.

You can also create private tournaments between you and your friends which seems a good idea - win money from your friends with your 'expert knowledge'!

Is anyone else playing?