Blender 2.61: Cycles Render Engine
It is still in development, and more production features are planned to be added, this can be considered as a first preview release.
GPU rendering makes it possible to use your graphics card for rendering, instead of the CPU. This can speed up rendering, because modern GPU's are quite designed to do a lot of number crunching. On the other hand, they also have some limitations for rendering complex scenes, due to more limited memory, and interactivity issue when using the same graphics card for display and rendering.
Cycles has two GPU rendering modes, through CUDA, which is the preferred method for NVidia graphics cards, and OpenCL, which is intended to support rendering on AMD/ATI graphics cards. The implementation of this is only in an experimental stage however, and rendering of an ambient occlusion like image is supported currently.
|Modern graphics cards are very powerful, but the hardware and drivers are still limited compared to CPU rendering. We're trying to push this forward, but inevitably some rendering features may not work on all GPU's.|
Cycles currently has only a limited amount of features, and it will be extended over the following releases to support more features and become more stable. If it's powerful enough you can use it, if not, Blender Internal will still be available for a long time alongside Cycles.