Mobs on Al'Kabor don't seem to forget players after three minutes or whatever it was later on EQPC.
Here, there are two ways to drop aggro with FD:
1) Instantly, when feign succeeds
All mobs have a chance to instantly forget a player who successfully feigns. I'd put the success rate in the 30-40% range. So if you've only got one mob aggro on you, you can keep feigning until you successfully drop aggro.
This doesn't work, obviously, if the mob is standing on top of you. It's also unlikely to work if you've got multiple mobs aggro, as mobs forget (or fail to forget) feigned players independently of one another, meaning that if three social mobs are aggro and two forget you, the third will still call for help and re-aggro the others as soon as you stand.
2) When a static mob returns home
Static mobs - i.e. mobs that don't wander - will forget feigned players when they return to their spawn points. Some static mobs start walking home instantly when a player feigns; others wait around for anywhere from a few seconds to an hour or more; and some simply never walk home. The final category of static mobs, like roamers, can't be ditched with this method.
So, yes, while static mobs are easy to ditch aggro on, if you've got a large number of wanderers on you, it's very likely that you can't drop aggro at all with FD. So, whenever possible, avoid aggroing large packs of wandering mobs and then feigning! If you've only got one or two wanderers on you, you can usually ditch them by feigning a bunch of times and counting on the innate "forget me" effect of feign. Otherwise, you'll probably have to /q, zone, camp out, or get a CoH to drop aggro.
, Swift Tail of Temerity
Soft-skinned alt scum: