This is obviously done with DirectCompute, which is a part of the DirectX11 API set. DirectCompute still fully supports DX10 GPUs so there shouldn't be any backwards compatibility issues in that regard.
I'm really looking forward to an IE9 Beta so we can try this out ourselves.

UserAgent: Mozilla/5.0 (Windows; U; Windows NT 6.1; en-US; rv:1.9.1.5) Gecko/20091102 Firefox/3.5.5 (.NET CLR 3.5.30729)


