Here in NZ we once had a prediction market where you could put money on your opinions about future events- it was established by the Statistics department of one of the universities- I think Massey but not 100% sure- anyway these prediction markets can definitely be of value and are not simply gambling. It was called ipredict and was so successful that a subsequent right wing government closed it down...or to be more accurate I believe it was forced to move offshore but have not heard of it for several years so they effectively shut it down in NZ- note polling is a strategic asset for political parties and the right wing government that shut down ipredict is closely aligned to several private polling companies....

However, aside from avoiding meddling politicians, these prediction markets need some degree of technical depth to provide the best results.

I have only so far tried Bitcoinpredictionmarket and find it needs to improve its method of allocating risk reward- currently there is zero incentive to place an early bet n any event and total incentive to wait until the last minute before the event closes. If you are making a prediction a long time in advance of any event the reward should be greater than closer to the event.