Luckily I'm still at the planning stage, no UGC problem yet.
I'm thinking of launching a new app where a single click share would be a feature worth implementing, but definitely not part of the core functionality. I'm trying to figure out if this feature is worth implementing at all, or it's just asking for trouble.
I guess the benefit would be possibly higher SEO / DR, as you'd have a lot of backlinks scattered around the interwebs. But then it can be misused and then all your domain can also be trashed.
I believe this is probably beneficial for bigger companies / VC funded projects where they have the resources for moderation.