Instant messaging is great for quick answers and responses, currently if I need quick response I use instant messaging, JIRA is usually too "slow". Bad side of using instant messaging is that conversation is not stored in JIRA...

I am thinking about solution when task could be turned in messaging mode, then you could see who is loged in JIRA, invite people to conversation about task, see who is currently typing and all conversation would be stored on task as comments.