A post on the GIMP users website points out that Ubuntu 10.10 comes with OpenCL support which means that multimedia or image processing applications such as GIMP or the GIMP plugins can use OpenCL (hardware acceleration) to get an amazing performance boost - the post says this could make the GIMP plugins 1000 times faster and even though it seems a bit unrealistic, it's still pretty exciting. However, it won't work with the existing plugins - they will have to be re-written to take advantage of OpenCL.
Please note: this will only work with the OpenCL driver shipped with Nvidia 17x+ or the ATI SDK (so you'll have to install the proprietary drivers). Also, you need to have a CUDA enabled Nvidia graphics card (G80 GPUs, 8xxx series) or ATI with Close to Metal (2xxx series) to use it.
For more info, see the post @ gimpusers.com.
Thanks to bhm for the clarifications