While open-source desktop graphics drivers are fairly common these days (sans NVIDIA's current lack of support), in the mobile space such drivers are rare. There's been vendors like Qualcomm and Texas Instruments that provide open-source kernel drivers, but the user-space portion of these 3D drivers remain closed-up. With the user-space bits being still locked up, the kernel-space side hasn't moved into the mainline tree per the integration requirements. Read the embedded Linux GPU mess and embedded GPUs on Linux remain a great big mess for more detail. The most widespread example of how the closed-up bits can cause problems is with Intel's well known Poulsbo platform that uses PowerVR graphics.
While it's previously been reported that an open-source PowerVR driver might be here in Q3 and Intel is working to improve the situation, are more vendors beginning to contemplate full open-source graphics drivers on the mobile front? While there isn't any news to break on that front today, here's a poll in the forums to see what the community is currently thinking. Feel free to vote and add your thoughts, if this is a topic important to you.
If you haven't already done so, also be sure to participate in the 2011 Linux Graphics Survey, which is particularly important.