Well... I would say that it was one part not knowing what to expect - was I just going to mingle in this house full of extremely bright people for a few hours? I wasn't sure I was going to know what to do with myself.

It was one part doubt about my own.. uh.. qualifications for being there. I haven't commented much on my main account, nor made a submission (I hope you'll forgive me for using a throwaway account for these comments). I'm a college senior whose done well in every class (from lit. to programming to organic chem. to math), but I don't yet have a passion, nor area of expertise, so I wasn't sure that I would be able to contribute much... or even last long (i.e. be able to carry on) in a conversation with the opinionated and up-to-date scholars there.

I guess the advice I would give would be this: cater more to shy / socially anxious people. Maybe have a snippet you can paste at the end of every announcement, just summarizing what goes on there and who all is welcome, what the ecology / environment is like, etc. Tell people what the sufficient conditions are for their being welcome.