Setting up a fine-grained permission system

Hi,

Our current project requires a fine-grained permission system (row-level
and possibly column-level as well). We have a pretty large (tens of
thousands) of users in the 'party' table. I'm thinking of choosing
Unix-style security for now (adding 'ugo' and 'owner' and 'group'
columns to each table which access need to be regulated), but am unsure
about the column-level permission.

Anyone has experiences to share on a similar system/requirement? Do you
do Unix-style or ACL? Is there a possibility in the medium/far future
that Postgres will have such a fine-grained permission system.

Regards,
Dave