As the title implies, I left the multiplayer lobby open, looked away, and missed people coming and going. I would have greeted them for a game had there been a user entering/exiting sound. Which is to say, I missed phaselock. We have a sound for when people post text, so how about for enter/exit?
Surgeonfish enters the thread *dun dun dun....* Surgeonfish leaves the thread *children screaming "yay!"*
Unless it's annoying it's pretty much standard! I'm really for it, but don't forget to include 'turn it off' option.
features in this regard could also include a soundeffect when people on your friendlist log on (if friendlists exist that is)