Mountain biking is all about concentrating and balance (other stuff too but these two are the ones that spring to mind for me). I tell ya, 100km on the road is often easier than 100km on the dirt!!!

You don't have to wear different clothing..jersey & shorts will do.

Many roadie techniques carry over to the trail-lean into the corner & look ahead. Picking the right line is often the trickiest thing. One false movement on a trail can mean running into a tree or sliding down

Mountain biking's heaps o fun and tons more fun than road riding. As Aggie Am mentioned in one thread, why do a century when there's dirt awaiting!