I got back into cycling in the late '80s on a Bridgestone mountain bike after a 15-year post college layoff. I live near the Tahoe Nat'l Forest and did mostly mountain biking for several years, but then fell in with a bunch of road guys and for about a dozen years have ridden the road almost exclusively.
We've had rain and snow for a few days, and this afternoon I happened to notice the old Bstone hanging from the rafters. I don't think I've even looked at it in five or six years. I hauled it out, lubed the chain, pumped up the tires and took off, just planning to ride around a little and loosen up. After a few minutes I turned up some once-familiar paths, did a creek crossing, all the stuff I used to take for granted. I learned a lot:
1. The hills are MUCH steeper.
2. My technical skills are gone. Probably permanently.
3. Wet rocks are slipperier, but not any softer.
4. It's still fun, but moderate road-bike fitness doesn't necessarily translate into mountain-bike fitness. I really thought i was in decent shape, but little sections of trail I used to manage without much difficulty stopped me cold.
Depending on the weather where you live, it might be worth hauling out that old MB and getting out occasionally. I was amazed how my bike control skills have suffered now that I don't use them anymore.