The answer to this chat-related question leads to a feature request:
A simple way to notify and invite someone to chat regardless of whether they've ever chatted before or not.
As a [stackexchange user] I want to [invite another user to chat] So that [we can continue our discussion easily]
ADENDUM: for archival purposes it might make sense to auto-create a room for discussions started in the comments of a particular question/answer. Yes, this effectively turns SO into a forum - but it keeps the discussiony stuff out of the main Q&A stuff, which I think was the point of having a separate chat system.