I didn't wear mine today. I wore, instead, a Very Cheap pair of cotton shorts, which couldn't have cost more than $6, over a pair of <gasp> conventional underwear.
Twenty mile ride.
What I noticed was these shorts didn't roll down my, um, slightly enlarged midsection like the fancy shmancy mountain bike shorts with the gel padding.
In fact, there was no discomfort whatsoever. The saddle felt the same as always.
Now, it's just one ride, but (and God help us if the Underwear Nazi is still around), I didn't see any advantages for the MTB shorts. In fact, what I wore was lighter.