If you have a revoked authentication subkey in your keyring,
monkeysphere gen-subkey thinks that I have an authentication subkey
already, which I do, but it probably shouldn't care about it, since it
is revoked:

     	 21:30@pond> monkeysphere gen-subkey F67E2A5D1CF2D62A
	 An authentication subkey already exists for key 'F67E2A5D1CF2D62A'.
	 Are you sure you would like to generate another one? (y/N) 

However: this key was revoked on 2008-04-28 by DSA key 1CF2D62A Micah Anderson <micah@riseup.net>
	 sub  1024R/866F47D3  created: 2008-02-25  revoked: 2008-04-28  usage: A   

I can continue to create a new authorization subkey, so its not a
blocker or anything (I suppose I could also delete the revoked key
from my keyring as well, although thats less than ideal).

It seems like the secret keyring doesn't mention that it has been
revoked, so probably monkeysphere needs to be looking at gpg's
computed validity from the public keyring instead of the secret
keyring to be able to get the "r" flag from field 2, in addition to
the "e" flag from field 12.