One oddity I saw on nouveau was this stack backtrace on exit:
[  1000.860] (EE) Backtrace:
[  1000.862] (EE) 0: /usr/X11R7/bin/X (xorg_backtrace+0x44) [0xd23b25c5]
[  1000.862] (EE) 1: /usr/X11R7/bin/X (os_move_fd+0x79) [0xd23ae365]
[  1000.862] (EE) 2: /usr/lib/libc.so.12 (__sigtramp_siginfo_2+0x0) 
[0x7a87b337e430]
[  1000.862] (EE) 3: /usr/X11R7/bin/X (DamageUnregister+0xe) [0xd235e092]
[  1000.862] (EE) 4: /usr/X11R7/bin/X (shadowRemove+0x33) [0xd2366596]
[  1000.862] (EE) 5: /usr/X11R7/lib/modules/extensions/libshadow.so 
(shadowRemove+0xb9) [0x7a87ab80502c]
[  1000.862] (EE) 6: /usr/X11R7/bin/X (xf86_cursors_fini+0x216) 
[0xd22e7ffb]
[  1000.862] (EE) 7: /usr/X11R7/bin/X (present_vblank_create+0x13c) 
[0xd23d7a59]
[  1000.862] (EE) 8: /usr/X11R7/bin/X (XFixesClientDisconnectInit+0x13d) 
[0xd2320e92]
[  1000.862] (EE) 9: /usr/X11R7/bin/X (dix_main+0x481) [0xd2255f31]
Not sure if that's a regression though as I don't regularly run X on 
that machine.