In this study we explore the impact of exposure to social annotation, embedded in online consent forms, on individuals' beliefs and decisions in the context of informed consent. In this controlled between-subjects experiment, participants were presented with an online consent form for a personal genomics study. Individuals were randomly assigned to either a social annotation condition that exposed them to previous users' comments on-screen, or to a traditional consent form without social input. We compared participants' perceptions about their consent decision, their trust in the organization seeking the consent, and their actual consent across conditions. While no significant difference was observed between actual consent rates, we found that on average individuals exposed to social annotation felt that their decision was more informed, and furthermore, that the effect of the exposure to social annotation was stronger among users characterized by relatively lower levels of prior privacy preserving behaviors.