I can't be too sure of the specifics, but our db admins decided against UUIDs after a few days debating and lots of coffee. We aren't using serial, but instead

I can't be too sure of the specifics, but our db admins decided against UUIDs after a few days debating and lots of coffee. We aren't using serial, but instead using functions to generate our own nextvals with the server IDs, epoch etc..., kinda the same way as Instagram (though, obviously our databases are no where near the same size). It came down to how much logic we were comfortable implementing in the schema from the start to avoid continuing complexity in the applications themselves.