S3 Graphics just released a WDDM 1.1 beta driver for Microsoft Windows 7 Beta. This driver is a quite basic one, with missing S3 Graphcis ScreenToys (Control Panel) and it's just for the 32 Bit version. So, the Release Notes mention several limitations. But since it's a beta driver and Windows 7 is also still beta, the feature set will surely increase in the coming months towards the final release of Windows 7.

Known Limitation (General Software):

• In this version of driver, S3 Graphcis ScreenToys is not included, and features as S3 MultiChrome/PanoChrome are not available.
• WEI performance score may not be stable for the test item of "Gaming Graphics". (41800)
• Desktop icons will move to extended display when change displays relative position (42072)
• Enabling duoview for the 2 output monitors connected causes windows aero effect become lost. The second monitor must be enabled as single view with primary monitor disabled before enabling duoview. (42591)
• Personalization Window corruption may occur when desktop color is changed from 16bit to 32bit. (42070)
• Booting into OS with no display monitor connected, if desktop mode was previously set to 1600*1024@32bit, hog-plugging display monitor will cause windows log-on screen shrink to the upper left conner of the screen. And if another desktop mode was set, then the log-on screen will automatically change to 1600*1024@32bit with full screen properly displayed. (42058)
• It takes the cursor several more seconds longer to correctly rotate, instead of rotate instantly, after setting 90 or 270 degree desktop rotation. (42709)
• Video playback may stop while audio contiues with player progress bar still moving under MAMM mode (multi-adapter multi-monitor), such as CRT connects to primary card and DVI/HDMI monitor connect to secondary card. (41905)
• Age of Empires II-The Conquerors Expansion: System hang occurs after starting a new game (42523).
• A common problem of mouse pointer being lost under full screen game mode occurs in some of the game titles:
  • Warhammer Online Age of Reckoning (42544)
  • Everquest II The Shadow Odyssey (42534)
  • Company of Heroes: Opposing Fronts (DX10) (42532) 
    

Known Limiations (App Specific Limitations/ Vendor Detection):

• Video playback becomes choppy while playing WVC_1 clip with Windows Media Player12. (42594)
• Screen will flash when switching from full screen mode to windows mode during WMV-HD playback under WinDVD9 (39802)
  

Links:
Release Notes
Driver Page for Chrome 500 Series 
Driver Page for Chrome 400 Series