On my Powermac 9600 running a fresh install of Gentoo 1.4rc1 from stage three, if any keymap is used other than the one compiled into the kernel, the keyboard (adb) is rendered unuseable. One "solution" (in the style of duct tape), is to avoid loading a keymap, by editing the keymap init script to not do anything. I have hit the same problem before with XFree86 keymaps, and the "solution" that I found to that was also to avoid loading any keymap, and letting it default to the one compiled into the kernel. I have tried using a keymap file directly from an old YDL 2.1 install, the exact file that was running it, but it also scrambled all input.
you might want to check that you dont have the 'enable raw adb keycodes' option in your kernel checked as they keymaps rely on using linux keycodes, see the install guide for more info on this
