I noticed this while pulling in the Cartheon Wing, and believe the machanism was introduced in one of the recent patches.
When mobs have been pulled >130m (or so) from where they spawn (or currently roam), they will lose all aggro and instantly teleport back to their spawn location.
So heres how the method works for splitting two mobs, CartheonA and CartheonB;

--The monk throws a shuriken at CartheonA, and they both come running.
 -the tank tags and aggroes CartheonB
 -the monk runs off in a direction with CartheonA, and it resets (as described above)

Just interested if anyone else uses this? seems to work well

Only problems i can think of are:

Limited by environment
Healer may get aggro on the mob monk is running with

Yes usually they would, but not if you do what i said above.
The whole mechanism only seemed to enter the game game recently (before mobs would just drop aggro and start to run back)
This really works, a single monk can do it, and it's less risky than 2 FDers.
In fact it doesnt even have to be a monk who does it

I just hope it's not considered an exploit

im confused by your pull method pusur. with your method , your pulling 2 mobs back to the raid. is that what your intending to do?

I pull with a necro in my guild, mostly because I like watching him die.  But they bring a lot to splitting too with their pets, ranged mez, and very low aggro spells.

I also split with a disciple on some pulls, and sometimes a dark knight if he makes me angry.

i like using a disciple, 1 min recast on fd means im 3000 time more likely to get a good laugh

We have a gnome necro, but for some reason he cant pull.  If you ask me he does bad on purpose so we wont use him ;-p   

My guild must do something really different, beside the inital elevator with 2 at top, we never have to pull or split pirates.

We kill a good 5-8 sky pirates but thats it.  None need to be split.