Welcome to the rest of the DIR-615 world. This is why I left over a year ago for a linksys (has worked since I took it out of the box and setup configuration for wifi and has never been reset). I had these issues, wifi devices not being able to connect, not getting IP addresses, would have to reset it just to get 30 - 45 minutes of connection and then right back. Figured hey, probably my device.... 2 iPhones, a Wii, 5 computers, 2 laptops all acting the same.
Dlink simply makes crap products, and has no care in the world to update them or fix these issues.