The reason HipChat and similar tools have such a hard time spreading beyond a relatively small group of people is because they lack federation capabilities.
it's a shame, because hipchat has massive advantages over both email and skype (list them)
why no federation, unexpected success, running against enterprise walls - jabber, lync, and ... email
federation-as-a-service -- why not? we're an independent entity, we exchange federation services for your money. we ensure our service is more reliable than hipchat and all other providers, so we can notify you when someone is down