I've been running version 1.2x (I forget which beta) for quite some time now.
However, I've got DNS relay disabled, as well as DHCP server, since I've got a linux box in my network handling DHCP, which also services DNS requests from network clients (rather than the '655), the DHCP/DNS server also bypasses the '655 by using a list of static DNS servers provided by my ISP.
The router only goes down when we lose power (in its current configuration).
Note that the seeming insanity of the setup was brought on by the need for gigabit router (the 655), -AND- working reliable DNS services (which I now have regardless of the network gateway device).
Before I gave up on using the 655 as a DHCP & DNS server, I experienced intermittent problems on various machines (windows, linux, and macs) in various ways, with DNS relay on -AND- off, though the problems would vary from sluggish-ness to failed resolves for things which CLEARLY shouldn't have failed, and some other strange behaviors.
Though, I suspect -PART- of the problem was the fact that the DHCP server on the 655 (when sending out DNS addresses to hosts as part of the DHCP message) would give out the address of 0.0.0.0 in addition to its own (or my static WAN-Side DNS server depending on the state of the DHCP relay setting). And as far as I could tell (not being a network expert by profession) this caused machines to intermittently be _VERY_ confused when they tried to ask 0.0.0.0 for a DNS resolve (I don't think they're SUPPOSED to be able to do so, but I suspect some were anyway).
Of course I could be mistaken about it handing out 0.0.0.0 as a valid DNS server through DHCP messages when DNS relay was on, though I don't think so. I am however *CERTAIN* that it did when DNS relay was off, it would mindlessly send both the primary static DNS address from the WAN port -AND- the secondary address without checking to see if they made any kind of sense first.
I'm happy with my current setup, though I also want to contribute to making the (otherwise very nice) router actually usable as a router by itself, without having to reverse engineer the thing's behavior.