I've had WP install setup to use Ping-O-Matic for a long time, but I don't think it's worked (properly) in ages. Some sites (Technorati, etc.) just don't get updated via Ping-O-Matic, although the settings appear to be correct (maybe it's an issue with Technorati's RPC?).

It's still in my Update Services settings, but I may go back to setting up pings for individual services.