As a user, I thought about two features you could add to the app:
• First, I was thinking that maybe the subconference buttons could be cumulative: you could choose to display all the droidcon and mascon sessions for instance, instead of switching the previous choice off when you select a different one.
• second, since the bookmarked sessions are saved on a backend, it could be interesting to see how popular a session is in advance (for attendees, you would know you need to hurry up if you want a seat, for speakers, you would have an idea how many people are interested in your talk).