Same problem : steam segfaulting at startup with xinerama enabled, working flawlessly without. (awesome not installed, so it must come from xinerama)
Mint Mate 13 x64, HD5870
Latest catalyst drivers (13.4 - 4/24/2013 release)
Xinerama is deprecated. Please use XRandR.
Closing as general video driver quality from 2013 is no longer relevant.
Nothing extracted yet.
The other day I was trying to get steam working, however was segfaulting.
I had xinerama installed for dual monitor support since awesome 3.5 requires it.
I installed awesome 3.4 instead because xinerama was giving me other issues.
Now I noticed steam started working. However I am not sure if it is because of xinerama or awesome 3.5 or something else. I will investigate when I have time however I thought I'd raise a issue here in case someone else is having the same issue.