Gamergaia previews[1] the upcoming New Vegas DLC Old World Blues, mostly by summing up known information. They put the release date at "June 14th, 2011".
Previous DLCs have kicked off with a new quest marker in the Mojave Wasteland leading to a point of no return, not allowing us to revisit the New Vegas map until we’ve completed the add-on’s quest objectives, so we can assume a similar plot progression for Old World Blues. It looks like gunplay and other technical aspects won’t receive any major upgrades, but that’s what we expect from DLC – seldom do add-ons make vital changes to established game mechanics (I was left gaping when Honest Hearts, using Skyrim’s new dialogue system, had Joshua Graham fluidly cleaning his guns as he spoke to you, rather than standing ramrod-stiff and staring soullessly at you as Fallout characters tend to do). New enemies are always lots of fun to discover, and the crazed “Lobotomites,” victims of experiments gone awry, sound like they’ll do justice to the series’s track record with horror.
You will not be stripped of your equipment, a feature of previous DLCs that had players (rightfully) up in arms, and as with all New Vegas add-ons, the level cap is bumped up by five to give you room to grow. You’ll receive a perk option to cap yourself at your current level, thus ramping up the challenge, as well as the opportunity to rework your character’s appearance and abilities in case your Courier is, like mine, horrifically ugly.