This paper examines social media users’ perceptions of simultaneous interpreting quality in a live streaming interpreting event on YouTube. On December 11, 2012, Harvard Professor Michael Sandel was invited by Taiwan’s Ministry of Culture to give a lecture about his new book, What Money Can’t Buy: The Moral Limits of Markets. The lecture was held at a stadium with an audience of 6,000 people. At the same time, the lecture was broadcasted live on YouTube, so simultaneously there was a group of online users listening to the lecture. Because the YouTube streaming did not provide dual channels, the online audience had no choice but to listen to the simultaneous interpretation, while the original source speech was broadcasted at the backdrop at a lower volume. In other words, online YouTube audience became default absent users of the interpreting service. Most importantly, the YouTube audience not only watched Sandel’s lecture and listened to the interpreters online, but many of them posted online comments simultaneously. The comments comprised the basis of this research. A total of 233 comments from 134 unique users were collected to form a rich set of uncontrolled, natural data on users’ perception of interpreting quality. This data was closely examined to understand the different quality criteria used by different users. Overall findings show that delivery-related criteria, as opposed to content-related ones, were most often cited by the interpreting users. Context does matter, so given the highly-interactive nature of the interpreting event, the data shows that users paid much attention to prosodic features, such as fluency of delivery, smooth alternation between source and target languages, and lively intonation. Technology is another important element in this research. New electronic media has enabled interpreting events to broadcast live on-line, expanding the number of interpreting users and also changing the nature of speaker-listener-interpreter relationship. Adequate technical support is necessary in this case to ensure the quality of interpretation delivery, otherwise technical shortfall affects users’ quality perception, as reflected in a large portion of comments that preferred listening to the lecture without the interpretation.