not a special post on the subject but for the purpose of any warlock that wants to search about this trinket, i did a small test and found:
*does not work on Fel Armor heal ticks
*does not work from Siphon Life heals
*does not work from Haunt heal
*although didn't test enough for Drain Life it did not proc
only procced from using Life Tap, it took about 7 casts to make it proc on occasions, even giving time of 1 minute for cooldown to go.
i only wanted to test because it had been bugging me for a while and i was able to refund for my badges at the vendor, but if you want an SP trinket get the Wintergrasp one and save your badges:
http://www.wowhead.com/?item=46081