It's been about 5-years, so I'm feeling it a bit now - and that's after a pretty casual ride(even after riding my MTB almost daily the last 4-months). I geared it up a bit though. It was 22/18, which is closer to a true/natural trials gearing, but I really prefer urban anyway. So I went to 22/16, and it feels like a decent gearing. The bonus was it allowed me to remove a link, which gave me the perfect chain length to run without a tensioner. 
I'm planning on bringing it to the Challenge for a pit bike this year, so I figure I needed to a.) make sure it was in decently rideable condition, and b.) get back in practice a bit, just in case an impromptu bunnyhop completion breaks out in the parking lot. 
Younger Me keeps wanting to bring my mountain bike to rallycrosses and play trials rider on peoples' trailers.
Current Me reminds Younger Me about our knees and ankles and wrists and how they are the reason the bike has been collecting dust in the first place.
I say DO IT!
Weird: I always preferred to ride in a 32/21. Not a trials bike of course, but I never much liked slow going with super low gearing.
In reply to Knurled:
The low gearing sure is nice when you're on obstacles out in the woods, but really doesn't have much benefit in town. Having low-ish gearing helps with pedal-kicks, but it has to be both low enough to be able to give you quick torque, yet also still provide some forward momentum.
That isn't what I pictured at all.
In reply to sesto elemento:
I definitely got some funny looks pedaling it to the post office & back.
Ah yes, my younger me says this looks fun. I rode modified trials for a few years.
sesto elemento wrote:
That isn't what I pictured at all.
This is what I was hoping for, too! WAAAAYYY back in the day, from sixth through 12th grades, my dad and I had a pair of Bultaco 350's with the interchangeable small and large gas tanks. We would fit the large tanks for mountain camping in Colorado and New Mexico. Best motorcycle camping trip ever was riding out of Crested Butte up to Copper Lake, elevation 10,100 feet. Loved exploring on the Bultacos, finding the roughest and biggest things to ride over. On the Copper Lake trip, we rode up to an ancient abandoned silver mine whose entrance was at 11,500 feet. The engines were starting to weeze a bit by the time we got up there! But the view, OMG!!!
I love watching trials riders. If I had seen that kind of riding when I was 10 I have no doubt I'd still be doing it. If I wasn't broken or dead. No matter how much I like technical mtb trails though, 40 is far to old to try learning trials.
Very cool that you can ride even some of that.
