Details are scarce at the moment, but Shinpei Kato was talking about GPGPU this morning at XDC2011 Chicago and mentioned this fact. Hearing this isn't new and it's been mentioned somewhat in the past, but hopefully before year's end we'll hear more information. Shinpei works with PathScale in this area and is also one of the developers working on the TimeGraph GPU scheduler.
This open compute driver was developed via reverse-engineering the proprietary NVIDIA driver. Its performance is said to be competitive with the binary blob. While the PSCNV driver is out there, this compute code apparently hasn't been pushed yet. It doesn't look to be open-source at this time. Shinpei said along the lines of, "PathScale is not yet aiming for open-source solutions until their products are released on the market"
While the code may not be out there at the moment, he's been putting out documentation. At the moment he says there's about 60% documentation coverage that's publicly available on the web for his work.
More details forthcoming.