I bricked my WRT54G. T'was a sad day. Well, to be honest, I didn't exactly "brick" it, I had openwrt on it, with no "boot_wait", and i had forgotten the ssh password to it. It seemed like the only option I had was do build a serial console for it, and solder it to the WRT54G board - which made me shudder. After googling for a while, I found an interesting article describing an "unbricking" method which worked for me. The whole presentation can be found at http://www.trilug.org/talks/2004-09-wrt54g/Hacking_The_WRT54G_Presentation.PDF .
Apparently, this is a dangerous procedure, which can result in a completely DEAD WRT, be warned.