I have a DIR-655 which was largely working ok with firmware 1.04. The only problem I was having was that if my cable went out, the router would constantly reboot until it came back, knocking all of my PCs off the local network for that time. Luckily, my cable is pretty reliable, so this wasn't much of a problem.
However, with firmware 1.05, it won't get an IP from my cable modem at all. I've tried power cycling the modem, resetting the router, toggling unicast DHCP on and off, and manually setting the WAN port speed to 10 and 100 Mbps. Still nothing. I have a Motorola SB5100 cable modem, if that makes a difference.