Today, for the 2nd time, I lost a wireless access point in the process of putting new firmware into it. The new firmware apparently has some problems, but that's to be expected as a risk.
I've only seen it rarely, but the right thing to do is to have a rom or small un-writable section of the flash that contains a fully tested minimalist new firmware accepter. So that no matter what you do to the firmware, there is some way to get the old stuff back in, through some use of physical switches. I know have to send this thing back for warranty repair over something that I should be able to fix here.
Now other than that the WRT54G is a fine wireless access point precisely because the firmware is open source and you can get fancy extra features from other folks, but because this means more updating, there should be an escape hatch.