After doing `M-x global-auto-revert-mode` in an emacs -Q session, if I eval
`(setq auto-revert-use-notify nil)`, auto revert starts working as before
(in emacs 24.4).

(Thanks to this comment on emacs.SE:
http://emacs.stackexchange.com/questions/10966/global-auto-revert-mode-doesnt-seem-to-work#comment17031_10966
)