We introduce the automatic analysis of conversational vlogs (VlogSense, for short) as a new research domain in social media. Conversational vlogs are inherently multimodal, depict natural behavior, and are suitable for large-scale analysis. Given their diversity in terms of content, VlogSense requires the integration of robust methods for multimodal analysis and for social media understanding. We present an original study on the automatic characterization of vloggers' audiovisual nonverbal behavior, grounded in work from social psychology and behavioral computing. Our study on 2,269 vlogs from YouTube shows that several nonverbal cues are significantly correlated with the social attention received by videos.