From what we have seen during the past 48 hours, even in periods where the servers were operating reasonably smooth, there seems to be no "idle log-out" mechanism in effect.
This may be convenient, since whoever is logged in is not forcibly logged out under normal circumstances, but it definitely does not contribute to the myriad of server congestion issues.
So, perhaps SE should enable such an option, logging out characters who have remained idle for a number of minutes, such as 10-15?