Yeah, that barrier is a tough one to overcome. We've found that having an easy entry point (nothing to install, one click signup etc.) lowers the barrier a bit.
Also having some kind of free tier could always be an advantage over hipchat...
Good point. The problem with a tier limited by the number of people is that you take away one of the best parts of a free chat service. Being able to freely invite _anyone_ into a conversation really opens up what you can do.
Also having some kind of free tier could always be an advantage over hipchat...