I have seen several threads about issues with Build 51, and I had some issues myself as well (wireless up and down every 30 seconds on WRT160N, wired ports disabled on WRT610N, bricked ASUS router). In all cases I was able to fix the issues by clearing NVRAM / resetting factory defaults, and then configuring the router from scratch again. I assume that this is due to the extent of the changes in this build (and hence incompatibility with NVRAM contents) - but hopefully this fix helps others as well.
Given this though, one question about a potential default configuration change. I know that this won't necessarily be well received, but could the default for remote access be on, perhaps with a non-standard port number (i.e. not 80, but maybe something like 8443)? I ask because I run 3 Wireless AP's (long story there, but to keep kids and wife happy with all their wireless devices - a very difficult IM job … :-)). The result of this though is that when I update a router, if I have to clear NVRAM, but the default is not to allow remote access … then I have to run around to each AP individually and connect wired to the LAN side of the router (which is a pain as they are in the attic, garage, etc.).