This paper reports on an experiment investigating how the number of simultaneous users affects the usability and user experience of a shareable user interface. Participants were instructed to complete individual drawing tasks on a shareable user interface running on a multi-touch surface table. The results show an increase in performance (shorter task completion times) correlated to an increase in the number of simultaneous users. No significant increase in user errors was observed when the number of simultaneous users was increased. However, despite these quantitative improvements in usability, participants reported that the tasks were more challenging when multiple users were working together.