I announced Movit today, my GPU-based video filter library. It's rather raw—for instance, the only documentation is a README file in the git tree—but it can do most of the basic things a user would want from a video filtering library, it's high-quality (fully gamma aware, weakly colorspace aware, floating-point throughout), well unit tested, and generally gives you ponies.
There is no client software using it right now, though, and the primary candidate (Kdenlive/MLT) does not seem to be very interested. But it's been a fun project to code on :-)
Update: Libre Graphics World made a much better post about Movit, with demo video and all. Cool!