The funny thing is that the PowerVR SGX series of tiny GPUs have been integrated in a tremendous number of very popular top-of-the-line smartphones! AFAIK, PowerVR is behind the iPad, iPhone, Motorola Droid, Droid 2, Droid X, the Palm Pre, Samsung Galaxy, Wave, and Galaxy Tab, many netbooks, etc.
PowerVR may easily sell as many GPUs as Intel these days (if not more), considering that mobile devices sell in far larger quantities than their more expensive and less convenient stationary counterparts. PowerVR had never been on my GPU vendor radar until this year, when I bought a Droid 2, and did some research, only to realize that TI OMAP and PowerVR are behind the surprisingly powerful graphics engine in this little smartphone.
I don't doubt that on Android devices such as Droid 2, there's a proprietary kernel module linked into the Linux kernel for the PowerVR SGX graphics. So I imagine it would be very interesting to a lot of people if a project were started to implement a gallium3d driver for some of the common PowerVR SGX cores. Admittedly, there would have to be quirks for the multitude of different applications of this core (e.g., there would have to be tweaks for differences between the SGX implementation in Apple A4, TI OMAP, and on the Atom netbooks), and the code would have to be cross-architecture, supporting at least x86, ARM v8, and Cortex/v9.
But -- if this could be accomplished -- it would be possible for open source enthusiasts to root their smartphone and possibly get an alternative graphics stack going based on mesa, gallium3d, KMS, etc. But then running the Android UI on top of that is another matter entirely....
I think the reason that Intel hasn't managed to ship a 100% working, open source, "Poulsbo" driver is that PowerVR/Imagination Technologies have been resistant to opening up a driver implementation on this popular core. Since they seem to have a relative monopoly in the small 3d-accelerated devices market, they probably want to hold on to as much of their unique "IP" (hate that term, btw) that gives them a competitive advantage, as possible.