In addition, we have repeatedly hit problems with our "mock" build system which uses a different kernel from what userland software is normally tested with. eg: [1] [2]. This stuff is going to hit Docker users sooner or later. It is also infuriatingly hard to debug.

[1] http://bugzilla.redhat.com/1062533

[2] https://bugzilla.redhat.com/563103#c8