This is in reference to the search application that is run when you click the "Search Active Directory" link in My Network Places.  Searching a Samba 4 AD yields 0 results, always.

Running Ethereal while attempting a search for a user shows that the search uses the following filter in the LDAP query:

(&(!(showInAdvancedViewOnly=TRUE))(|(&(objectCategory=person)(objectSid=*)(!(samAccountType:1.2.840.113556.1.4.804:3)))(&(objectCategory=person)(!(objectSid=*)))(&(objectCategory=group)(groupType:1.2.840.113556.1.4.804:14))))

Of note:  objectCategory is, of course, syntactically a DN.  Apparently AD allows the query filter to be a string containing just the CN of the object category, which Samba 4 doesn't yet do.