Something very useful that many fitness forums support is a place where users can post their form check videos for others to critique (such as the technique subforum of the Starting Strength forum). On the one hand, this is a great way to get feedback on your squat technique, POSE running form, yoga moves, etc, and useful as a long-lived resource that others can use for reference in the future. On the other hand, these sorts of posts have the potential to clog up a Q&A site and make all other types of content hard to find.
Thoughts?