Limitations:
* Smoke/Fire rendering is *not* supported on GPU yet, that is also documented here: http://wiki.blender.org/index.php/Doc:2.6/Manual/Render/Cycles/Materials/Volume
* Decoupled Ray Marching is also not supported yet, so no Equi-Angular and MIS sampling yet.
Note for Builders and Developers:
* Make sure to use the CUDA Toolkit 6.5 from now on. 6.0 might still work, but can cause slower renders.