I've just modified Unity.ad to hold the attributes uidNumber, gidNumber, and uid in the global catalog, using the info from http://support.microsoft.com/kb/248717

The "global catalog" is a partial replica of the account information needed to log in to the domain, used for performace so that users don't have to chase referrals when trying to login.

These particular attributes are used by Samba, in particular the 3.3 release that we're migrating towards, in identity management between the AD domain and the posix world.