My WRT54GL router had stopped working today morning and I had to restart it. After that I didn't get the DNS servers and as a result couldn't connect to the Internet.
I have to clone my PC's MAC to the router so that the cable company allows me access to the Internet. Upon accessing the router admin page, I realized that this setting had reverted. Once I cloned the MAC again, I could get a DNS server and connect to the Internet.
I was surprised by this behavior - I know the router has problems under heavy traffic (probably that is why it stopped working in the first place) but I would have assumed that the settings were in some NVRAM and was safe from poer cycles.
At some point I should try the open source firmware for this router. Since it has a Linux kernel released under GPL, there is a lot of cool stuff that can be done to improve it.