While trying to restore the original firmware of my WRT54G (v5), it actually got bricked. I was doing this so I could sell it... guess it won't happen any time soon.
I did follow the procedure but there was something abnormal with it. While restoring the original firmware, the light were supposed to stop blinking after a couple of minutes, but in my case, it was still blinking after more than 1 hour, so I decided to unplug/restart it, even if they were telling not to do so.
I have heard there's way to unbrick it, but I've never looked further.