Has anyone been banned for using Perform yet?

[Zarabeth]

Technically, naming your character Cloud Sephiroth and Sasuke Stark is a bannable offense. Realistically, though, it doesn't happen.

As has been said to death... SE's just covering themselves. As long as the copyright holders aren't complaining, nothing will happen. But SE does have to put those notices up so they are covered.

Character names would be a trademark, not copyright, issue.

As stated in the Live letter announcing Perform's release:

However, please make sure to perform music that is FFXIV-related. We don’t mind if you’re using it for personal use; however, if songs and music from other titles are being recorded and uploaded frequently, we may have to remove the feature, so we would like to ask for everyone’s support...

Also, SE could technically pull any video containing any scenes, screenshots, music, etc. from the game.