Online social media information is often used as a proxy for unavailable or partially observed data on networks of offline contacts. This, in turn, requires an understanding of how close the proxy online structure is to the "true" offline social network. Social media tools such as Meetup that collect information about both online networks and their offline counterparts are of particularly importance as they shed more light on the (dis)similarity of online and offline contacts and highlight its potential causes. In this paper we examine structural (dis)similarities of the Meetup online and offline data, with a particular focus on geographical differences. We introduce a new measure called the event score to assess connections made by the most socially active individuals, or social butterflies. We apply the new social activity metric to determine which sorts of events are attended most by social butterflies and to evaluate how this aspect of the network structure differs across US cities.