I've already found at least one probable firmware issue with the NVG510 Residential Gateway (RG), ajcherry. I'm using the IP Passthrough functionality. According to its own instructions on the right-hand side of the tab, the RG is supposed to pass its public IP address through to another device, using its own DHCP - but it won't do it. I had to manually enter the information into my regular router (an Airport Extreme Base Station, aka AEBS) to use the Passthrough functionality.

I actually called Motorola to ask them questions about the NVG510 RG. They said, yes, that this is a new RG, and that it's designed specifically to AT&T's specification, not Motorola's usual setup. In researching my question, they were surprised to find that the NVG510 and the 2210-ATT1 RG, both AT&T U-verse-specific RGs, were designed without a true bridge mode. They said that was definitely not a usual Motorola thing.

As for my not experiencing the issues you and others are finding with the NVG510's DNS, maybe my use via the IP Passthrough is allowing the DNS to work as it should. Again, I didn't manually enter the DNS settings into my AEBS - I just have the NVG510's IP address in the DNS textbox as automatically passed by the NVG510. However, maybe using the IP Passthrough functionality is bypassing or unblocking something that's blocked occasionally with high-load pages... Hmm...

In my case, I already had the AEBS with all the settings I needed. The NVG510 is very basic in some ways, and can't do some of the things I wanted to do (use fixed IP addresses, for example, via DHCP). The first method I used to "bridge" the NVG510 left everything locking up once there was a load on my network, so maybe that was because of the DNS problem. However, when I realized how to set up the IP Passthrough, that worked magnificently, and has continued to do so overall. Here's a link to my IP Passthrough "bridge" solution for the NVG510 with an AEBS. I would expect that a router-knowledgeable person could translate the AEBS instructions to the router of their choice:

http://forums.att.com/t5/Features-and-How-To/NVG510-Bridge-Mode/m-p/2928989#M29846

Oh, and obviously, this isn't going to help those who don't have (or need) a 2nd router on their network. For people with only a NVG510, I would recommend entering the DNS values manually on each of their computers, as Colin described in early posts on this thread. For people who have a 2nd router, but have put that router into bridge mode, I would recommend manually entering the DNS values into their bridged router to see if it helps.