Earlier this week I wrote and showed the messy Nouveau situation with Mesa 10.3 + Linux 3.17 Git -- window bars were corrupted and rendering oddly along with other on-screen problems. Fortunately, through the forum comments it was solved.
Upstream Nouveau was unaware of this issue that was affecting my entire assortment of NVIDIA GeForce hardware so it was then quickly assumed to be an issue with the Oibaf PPA that constantly is packaging the latest open-source Linux GPU drivers. On top of mainline Mesa Git, recently there's been the the Gallium3D Direct3D 9 patches (Gallium-Nine). While none of my testing was relying upon the Gallium-Nine D3D9 support, it was wreaking havoc on the system anyhow.
As of earlier today some patches were backed out of the Oibaf PPA and since getting back closer to Mesa mainline the Nouveau problems are a matter of the past. With that said, now I'm in the process of running some Nouveau Steam/Source Engine Linux gaming tests similar to today's 20-Way Radeon Comparison With Open-Source Graphics For Steam On Linux Gaming.
On Linux 3.17 and Mesa 10.4-devel I was also planning to run some open-source NVIDIA driver tests of the GeForce GTX 750 "Maxwell" graphics cards given their recent, reverse-engineered support, but as my latest problem, upon booting up the GTX 750 / GTX 750 Ti I am now greeted by no display output with the Nouveau DRM driver on Linux 3.17 Git.