Nvidia's first GeForce R300 drivers have received Microsoft's approval, bringing a slew of new features and improvements, including some added since April's 301.24 beta. In case you missed that pre-WHQL update, it introduced various technologies such as FXAA, Adaptive VSync, Frame Rate Target as well as Surround support for all GeForce 8 series and later GPUs. Nvidia explains those features in detail.
The 301.24 beta also introduced various Surround improvements for multi-monitor users, such as the ability to enable a fourth "accessory display" for basic tasks like checking email and Web browsing, maximize applications to a single display when in Surround mode, "peek" behind monitor bezels to reveal obscured menus and game information, confine the Windows Taskbar to your center screen and more.
GeForce 301.42 WHQL contains and even tweaks some those features while improving support for GTX 600 cards (including GTX 670 4-way SLI) and half a dozen 3DTV displays, as well as fixing a plethora of single and multi-GPU bugs. You'll also find new or improved SLI and 3D Vision profiles for many games, especially new releases like Max Payne 3, Dirt: Showdown, Sniper Elite V2, and Street Fighter X Tekken.
On top of all that, folks coming from March's 296.10 WHQL build will see performance increases in various titles. Depending on your card and configuration, you can expect gains of up to 23% in Skyrim and Just Cause 2, 17% in StarCraft II, 14% in Far Cry 2, 12% in Bulletstorm, 11% in Civilization V, 9% in Batman: Arkham City, as well as 4 to 6% in Deus Ex: Human Revolution, Dragon Age II, Metro 2033, and Total War: Shogun 2. Those boosts were recorded with GTX 500 cards, often in SLI, so your mileage will vary.