Using a configuration generated by xf86config, setxkbmap gives an error
every time it is run that is something like (I don't want to go back to my
old configuration right now, but this is based on my memory, enhanced by
'strings `which setxkbmap`'):

  Couldn't interpret _XKB_RULES_NAMES property

The problem seems to be that xf86config generates a line at the end of the
keyboard section like:

      XkbKeymap   "xfree86(us)"

whereas Xconfigurator, in that same place, generates:

     XkbKeycodes     "xfree86"
     XkbTypes        "default"
     XkbCompat       "default"
     XkbSymbols      "us(pc101)"
     XkbGeometry     "pc"
     XkbRules        "xfree86"
     XkbModel        "pc101"
      XkbLayout       "us"

setxkbmap works like a charm when I change the first line (as generated by
xf86config) to the above 8 (as generated by Xconfigurator).