We mentioned last week that a new over the air update for the T-Mobile G1 was on its way. It was called RC28 and was to address a bug with the Amazon MP3 store and offer a few enhancements. Well, since the Android browser security flaw was found, Google and T-Mobile have halted the RC28 update that was already in progress and will instead be sending out an RC29 update that fixes the browser security hole.
The new RC29 update started going out to users as of this past Monday.
You can find slightly more information on RC29 and future updates from the T-Mobile Forums.