From the most e-mailed stories of the day to the most favorite stocks of the week, Web interfaces are rife with cues conveying other users' ratings and reviews of products and services. Do these peer opinions indeed affect our decisions? And if so, are they as strong in their impact as cues conveying authority/expertise (i.e., high source credibility)? We explored these questions through an experiment (N = 243) guided by the heuristic-systematic model in social psychology. Bandwagon/peer cues are generally more persuasive, but when they are inconsistent, the authority cue influences decisions. In general, task involvement promotes systematic processing of these cues. Interestingly, we found no difference in perceived authority between CNET Editor's Choice seal and a seal from a fictitious "authority" (Zig!), among other indications of heuristic processing. We discuss design implications for user interfaces in general and recommendation agents in particular.