Talked about recently was a Portal 2 issue where a segmentation fault would happen when SELinux was enabled. This SELinux issue came down to some MP3 code used by Valve in Portal 2 that interfered with Security Enhanced Linux and so for a while Valve was recommending users disable SELinux. This, of course, mostly affects RHEL/Fedora-derived operating systems where SELinux is shipped and enabled by default.
For those users who were upset with having to disable SELinux, Valve has now updated Portal 2 so all the code is SELinux-compatible, and it also takes care of a temporary workaround from a few days ago where execution permissions were needed for /tmp.
SELinux gamers in need of more details can find the information via this GitHub issue thread.