Z has a great article on what SP1contains for the SDK, SimConnect, and 3rd party developers here.

I’d like to point out a few of the key fixes that will affect flyers:

Graphics:

·         Virtual Cockpit Lighting
Re-enable the ability to define gauge lighting as a single texture mapped 1:1 with the gauge texture map as was available in FS9.

·         Emissive Textures
The default emissive “Additive” mode was shipped with a bug where these textures would not display during the day. The documentation was also incorrect, in that it indicated this was the mode that should be used to generate nighttime textures. In order to maintain backwards compatibility with FSX RTM, we elected to keep the behavior of “Additive” (now called “AdditiveNightOnly”), and add new modes for “Multiply.”

·         Round Earth Corrections
Made significant progress to try to better map large, legacy add-on scenery to correct for the new round Earth modeling in FSX. NOTE:  There will still be some problems seen with this, but we've done our best to minimize the visual artifacts.

 

·         Autogen Lighting
We had a bug in the way roof textures were lit during the night in certain areas. They should now not "glow" like in FSX RTM.

 

  • Landing Lights:  Back-compat for FS9 style landing lights is fixed, along with better night lighting support for AI aircraft.

Terrain and Scenery:

  • Alpha-blend Threshold:  Fixed problem related to black "lines" around legacy autogen scenery edges.
  • Runways:  Support for FS8-style “invisible” runways.

SimObjects:

  • Texture.cfg:  Re-enabled support for aliasing SimObject textures.