A friend of mine experiences the following behaviour while using a macbook quite normally (no heavy loads, etc.). She is returned to her log in screen and apparently logged out, because after logging in again all applications are closed and sometimes work is lost.
The problem happens approximately once a month for a few years now.
The problem persists after updating to Maverick
I would say there is no issue with a full disk or excessive RAM demands by the programs in use. (mostly browser, skype, etc