Last May, DD-WRT released the (long in development) v24 of their firmware. I had been running one of the release candidates for it on my Linksys WRT54GL, but decided today to upgrade to the stable release. I downloaded the appropriate file (dd-wrt.v24_std_generic.bin), followed the instructions for flashing through the web GUI, and promptly bricked the router.
It wasn’t totally destroyed. I could still ping the router, but couldn’t access it in any other way. The power light would flash repeatedly, and no other lights came on. No amount of hard resets would fix it.