Hiya - Aquarin... ICQ, Skype et al, log everything. We don't. The privacy policy is simple: end conversation, end all data about it as well.
Additionally, I encourage you to try the service in "Sudden Death" mode with someone you know - whoever is in one of those conversations can terminate it at any time resulting in everyone losing the conversation simultaneously.
This is very different from a user simply exiting IRC or leaving an ICQ chat or having a pseudo-offline conversation on GTalk!
