It might be good to brainstorm a few topics of conversation; ones that won't alienate people who are relatively new, but will also engage OB/LW veterans. The Singularity can be a bad call because it usually boils down to inside view / outside view considerations that are hard to navigate real-time: conversations dissolve into debate instead of truth seeking. That said, with the right atmosphere it can be a great topic. Cryonics can be interesting but often isn't. If people have expertises they'd like to share that's often interesting if groups are smallish (less than 10). Conversations about group epistemology (the Bayesian Conspiracy, the Cooperative Conspiracy) can be fun if they lead to real insights or action. Of course, meandering conversation can be great too.