Bungie has announced that the first Halo: Reach playlist update has been "successfully deployed" to Xbox LIVE, which will correct a number of known issues while also "tweaking some of the existing core gametypes and playlists".
The list is rather extensive, so pop along to the Bungie site if you're interested in perusing them. Major changes include the removal of the SWAT gametype from Team Slayer and the addition of a dedicated Team SWAT playlist.
Also mentioned in the update is that campaign matchmaking will be added later this month (either October 12th or October 19th). Bungie reportedly held off including the feature at launch in order to give players enough time to play through the campaign without fear for the spoilers that may result from campaign matchmaking.