Vine just received a major update today to include support for iPhone's FaceTime camera and mentions. 

To enable the front-facing camera, tap the button in the far left corner. To mention other users, just type @username and select the name among the mentions you see. For example, typing @Chris will pull up Chris Hardwicke, Chris Fry and others. 

You can check out the update on Apple's App Store

[via 9 to 5 Mac]