I've written a PHP extension capable of running Pixel Bender kernels (Flash-compatible ones). Performance is not great, as it's not multithreaded and doesn't make use of the GPU, but it can typically process an image in fraction of a second. Compiling to native code using gcc reduces this time further.
It's something that opens up new possibilities for Pixel Bender, I believe. You can allow end-user to interactively adjust the parameters to a PB filter, with immediate display of the outcome. The final parameters can then be sent to the server and which apply the effect to the stored resource (an image or perhaps a video).