Thanks to the increasing popularity of mobile devices and online social networks, mobile and social video is on the rise, calling for a better understanding of its usage and future impact. In this paper, we provide an in-depth measurement study of Vine, a mobile application that is used for creating and sharing short looping videos of up to six seconds in length. Based on a dataset of 851,039 tweets containing a Vine URL, we investigate different aspects of Vine, including hashtag usage, video popularity and user attention. For the dataset used, we find that 34% of the Vine videos contain at least one hashtag, a percentage that is four times higher than the percentage of tweets that is in general annotated with at least one hashtag. In addition, we can observe that a Vine video that is shared frequently on Twitter within hours after its creation will have more likes on Vine after one week, compared to a Vine video that is not shared frequently on Twitter during this same period of time. However, we cannot establish a clear link between the number of tweets sharing a Vine video and its resulting popularity. Finally, by analyzing the evolution of the number of likes and the number of shares received by a Vine video on Vine and Twitter, respectively, we can conclude that a Vine video receives most user attention shortly after its creation, with the amount of user attention received not stopping completely but remaining stable for days to weeks after its creation.