Recently, I've had a couple problems with my DIR-880L unit. Running the latest 1.05 FW.
The first is that sometimes after rebooting the router, it will not allow any wireless devices to connect to the wifi networks, either 2.4 or 5 GHz. And in the off-chance that it does let one connect, there will be no network connectivity, either to the internet or the router itself. In this case, I would have to keep power cycling the router until it works properly again.
Another is that the 5GHz band isn't working how it is supposed to. It used to work fine, but now even if a client connects with a good link speed, the total download speed that it can get is around or under 10mbps on a 100mbps connection. 2.4 can achieve this fine, most of the time.
QOS also doesn't seem to work properly. By even having it enabled, it causes wireless clients to keep disconnecting and re-connecting to the internet, but they stay connected to the network properly.
I've had the router since April of this year, but I don't know how long D-Link's support/warranty lasts.