The most appealing and inviting thing about Vine for me is its flat pixel design. There was a great article and debate about flat pixels / skeuomorphism a couple weeks back --> <a href="http://news.ycombinator.com/item?id=5204380" rel="nofollow">http://news.ycombinator.com/item?id=5204380</a>
Vine is ok but you can't say it shines in terms of usability. The major issue is the tap to record. As most of the iOs users are taping to focus, you are basically going against a natural behavior for a camera type app.
I'm curious about their hand-holding UX approach. It worked for me. But I don't know if it's something that helps most users, or just gets in the way. Would be great to be able to A/B test something like this on mobile.