Hi,
Today I updated our samba server to 3.0.20b with samba debian packages. After upgrading, everything but uid,gid<->sid conversion worked. wbinfo -U/-S/-G were no longer successfull. 
Our setup is as follows:
All our Windows users are also avaible to unix with the same username via nss_ldap. So Samba should only lookup the username via nss and msrpc do the conversion afterwards. Due to the fact that we use no dynamic mapping between uid,gid and sid "idmap uid/gid" was left empty up to now in smb.conf. 
And this lead to the failure: 
The new winbindd implementation requires in the function winbindd_param_init in the file nsswitch/winbindd_util.c the presence of these configuration options, otherwise main in winbindd.c sets the winbind daemon in a proxy_only state, in which he doesnt do any conversion!

Resolution:
Setting "idmap uid = 999-1000" and "idmap gid = 999-1000" solved the problem for the moment for me, but i think requiring this parameter is senseless.

Thanks
christoph