With Flash 10.1, Adobe allows for decoding of H.264 encoded flash video to the GPU. The theoretical advantages of this are fairly obvious. It has long been know that playing high-resolution video of any kind is very difficult without using a GPU even when a very powerful processor is used, and Flash is no different.
Currently, Flash 10.1 is supported by any Nvidia card built at the G80 line. This means that everything from the Geforce 8 series except for the GTX, GTS, and Ultra is supported, as well as all new GPUs. This includes Nvidia's Ion graphics, which is good new for small PCs.
On the AMD side, all HD4000 and HD5000 series GPUs are supported, as well as HD3000 series integrated GPUs (but not 3000 series video cards). Both Nvidia and ATI state that the newest available drivers fro their cards should be downloaded in order to support Flash 10.1.
Intel's modern integrated graphics solutions should also work with this update, although Intel has not announced any official list of what will and will not support Flash 10.1.