First thing, I'm sure you're doing a Save Settings on each Setup page you do a configuration add/change in - Network Setup, Wireless Setup, Image Setup, etc. Next should be to do a Save Configuration. The button for the save is found under Maintenance/System tabs. The "Maintenance" tab is between Setup and Status across the top and "System" is in the left-hand column. "Save Configuration" is the top button.
I haven't had any problems of losing configurations on my devices when plugging/unplugging. If I did then at least I could restore from a saved configuration a lot quicker than hand entering each time.
As far as the DIR-615 goes I guess I would try a different router (borrow one? or, go to a friends house and try on theirs?) to see if I still had a problem. If yes then it's the camera, if no then it's the router.
ken
dcs-930
dcs-932L
NetGear N