As of late (which would mean in the last year), I have seen a marked growth in interest in mountain biking, and cycling in general. Just today, I took a friend to the LBS to purchase his first mtb in 15 years.
I have started seeing newer riders on the trails. Some are out there for the fun, some for fitness. I've met folks who are actively involved in other sports but are just looking for another avenue to have fun with. I have met more than a few motocrossers who have dropped the gas-powered circuit for the pedal-powered.
Since I also ride road bikes, I've noticed even more roadies, especially in the local group. There are more and more new riders joining. Some are older and are returning to 'active duty'. Some just want to gain fitness, although many are fearful of riding on the roads alone.
Over the last year, I heard so many times that with Lance Armstrong's retirement, the sport of cycling would deteriorate. However (and fortunately), it seems the wave is rolling in the other direction.
As we toured four of the LBS's, I noticed that each of them were stocking more and more. Granted, road bikes were more prominent than mtb's, but it was great to see these businesses flourishing.