Honestly...most MMOs I've played that had tab targeting have all pretty much had the same issue. And that is, simply put, it didn't work worth a plug <bleep!>.

"OK! This one's dead. Time to move to the next *tab* targ-wait. No...not that one. *tab* Eh? Seriously?? He's like 50 friggin feet away! *tabtabtab* No. No! NO! *tab* OMFG REALLY? That's not even on my freaking SCREEN! SCREW THIS! *click* That guy, THAT G-oh great...he's friggin dead and now I gotta go through this crap again!" <Goes into a rage storm that would make both the Tasmanian Devil and Animal go "Whoa, Dude! Calm down!">