BTW, some people on the German Wikipedia are complaining that they are getting logged out after a few hours. I remember that there was some discussion about this problem some time ago, and I thought someone had fixed this. Or is this again a browser problem?
You have to check the 'Mein Passwort merken' checkbox in the login screen. Maybe this checkbox should be placed near the 'Anmelden' button and not near the 'Neues Benutzerkonto anlegen' button to be better noticed.
WeißNix