I have been using a Linksys E3000 since Fall 2011. My Xbox is in the DMZ and has a static IP. UPnP is enabled. For at least six months my NAT was always open. Then after a dashboard update I started noticing my NAT type would change frequently. Yesterday when I signed in my NAT was open for the entire session. Today it is moderate. When I was playing more often It would easily switch a dozen or more times throughout the day.