Valueman, I have dabbled with tradesports.com
Great software, looks like a very professional operation.
I love the concept, especially real time interactive trading with the games or tournaments (golf).
However,the spreads by the market makers are WAY too wide and there's not enough volume for anything more than casual wagering.
For example, take a golf tournament... you've got Mickelson and Garcia five strokes back in the second round. You'll see the bid at 2 and the ask at 4. Now that's crazy. Furthermore, if you're paying juice on the number of shares, you get hammered on the trading of the very low numbers.
Still, I look for this to become more popular in North America once interactive TV becomes ubiquitous. When you can bet on FG being made on Monday Night Football on your TV set, whoa, the party has really begun, lol.
I know that's not really exchange trading in the sense you meant (person-to-person betting), but I've had a couple of brews, so please excuse.