Xin Shuai, Alberto Pepe, Johan Bollen have self-archived "How the Scientific Community Reacts to Newly Submitted Preprints: Article Downloads, Twitter Mentions, and Citations" in arXiv.org.
Here's an excerpt:
We analyze the online response of the scientific community to the preprint publication of scholarly articles. We employ a cohort of 4,606 scientific articles submitted to the preprint database arXiv.org between October 2010 and April 2011. We study three forms of reactions to these preprints: how they are downloaded on the arXiv.org site, how they are mentioned on the social media site Twitter, and how they are cited in the scholarly record. We perform two analyses. First, we analyze the delay and time span of article downloads and Twitter mentions following submission, to understand the temporal configuration of these reactions and whether significant differences exist between them. Second, we run correlation tests to investigate the relationship between Twitter mentions and both article downloads and article citations. We find that Twitter mentions follow rapidly after article submission and that they are correlated with later article downloads and later article citations, indicating that social media may be an important factor in determining the scientific impact of an article.