Patch 4.0.6 (8-Feb-2011): Cooldown was increased to 15 seconds, up from 8. Devour Magic is no longer able to be auto-cast.
/Patch 4.0.1 (12-Oct-2010): Devour Magic no longer removes a harmful spell from a friendly target. (Not entirely certain in which patch this change was actually implemented. This patch is an estimation from what info I could find.)
Patch 1.2.0 (18-Dec-2004): Fixed a bug where the felhunter would be healed every time the spell was used, in addition to the healing gained from successful dispelling.