google 'plyometrics'... there's plenty of info on it. I think it's generally associated with increasing speed and explosive strength (i.e. fast twitch muscle fibres), it has less of a benefit for endurance runners. Ultimately it depends what distances you're running!
By the way... you could get the same sort of gains from similar plyometric exercises that don't require the use of such elaborate equipment.... Oh, and trampolines bloody hurt when things go wrong!