It seems that T-Mobile has just started pushing an over-the-air update for the Samsung Vibrant Galaxy S phone. The update reportedly enables Samsung Media Hub, adds a Task Manager, creates an HD Camcorder icon and fixes the GPS problem. I haven't gotten an update notification yet on my Vibrant, but I'm always the last to get these Android updates from T-Mobile. And no, there's no way to manually force an update and no PC download file available yet. T-Mobile states that the upgrade will run through the end of October and will release in staggered waves.
There are discussions on T-Mobile's own forum about the update. T-Mobile's Facebook page has an announcement about the upgrade as well.