Charms of Luck say they will prevent drops from "Boss / Raid" fights. Yet many people have said that the Charm of Luck does not work with Baium, Antharas, and Valakas.
I am positive it does work on epic bosses. My alliance altogether took hundreds of deaths to Antharas and we didn't drop a single item (not counting a drop from one char who ran out of his luck charms and died again before he could resupply from our officer). The six or seven deaths I took -- sure, that could be a coincidence -- but hundreds without a drop?
If you drop when you have a luck charm, to a boss or raid boss, you should petition it as a bug. The description also specifically states "boss OR raid battle" implying there are two separate conditions for which it is useful.
This was asked a long time ago already, and we had an official response. It was about a year back or so, so I cannot find the post anymore since it went poof. But one of the officials submitted the question to the devs, and the answer was that the charms do not work on the epic bosses (I still remember it so well since there was a discussion about why the description then mentions "raid boss and boss fights"). Maybe they changed it in the meantime, after all we have had lots of changes since back then. So it would be interesting to hear an official answer about the current status.
The Antharas raid I mentioned was in C4. And I'm absolutely positive that the charms were functional then; the amount of deaths we took without drops was much too high to occur by chance.