Or do you think it's overblown and an overused term?

It's very real.
Cats will definitely try to block your progress, if they have the means to do so. We saw that with Irv and 50. Dude was actually makin' calls, tellin' people not to fukk with 50. mad personal. I don't believe in fukkin' with another man's money, so I didn't agree with that at all. Irv actually came out later and admitted that he was tellin' people not to do business with dude. So Em and Dre dealin' with him was HUGE! That cat's success was karma!!
But the "blackballin'" shyt is also an excuse for wack rappers who just can't get a deal. They'll swear someone's holdin' them back, when in fact, the only thing that's stoppin' them from movin' forward is a lack of talent.
runs this shyt.