Created attachment 105418 [details]
Instantly after opening Steam X crashes. OpenGL apps work fine, tested with Unigine Heaven (64 bit) and Xonotic (32 and 64bit).
Created attachment 105419 [details]
Forgot to add, system is Ubuntu 14.10.
Just a guess but this might be duplicate of bug 78604 as xserver 1.15 can crash with gcc libraries steam provide.
Yep, update to xserver 1.16 solved this. Hopefully xserver update will and in 14.10 before release.