Mountain bikes have contributed so much to bicycle technology over the past 20+ years that it's hard to over estimate their influence on all of cycling. The whole sloping top tube geometry that is predominate in road bikes today came from MTBs. The stresses that bicycle components have to withstand on the trail has undoubtedly led to lighter/tougher components in general. You can't be a bike weenie and not be utterly fascinated with MTB technology. The fact that state of the art hard tail MTBs now routinely weigh 20-21 lbs, and full suspension rigs 23-25lbs is remarkable when you consider their capabilities. My new hard tail with the disc brakes and SID fork is similar in weight to bikes that were winning the Tour de France in 1970. That's too cool.
I recall when I first rode V brakes, they were amazing. Now it's disc brakes. The gear just keeps getting better. Very, very cool indeed. Whatever you think about mountain biking, it's a fascinating gear-fest that road cycling can't really match. Like some bizarro cross between cycling and off road motorcycles.