I haven't used it before, but I experimented with Youtube links when I read an article saying that channel links were do-follow. Apparently that was back in 2010 though, and now they've made it nofollow.
But Youtube is one of those sites that unless you're trying to drive direct traffic from your videos, in my opinion it's far more trouble than it's worth as a source of nofollow links - especially when sites like Twitter and Facebook are much more manageable.