Phillip Seymour Hoffman was addicted to Heroin.. that's the only exception I can think of though.
Now.. pain pills, that's a whole different story. But, really, there's very little difference between things like percocet and heroin (other then dosage amount). One is just more socially acceptable. If you took 20 percocets, it'd be the same high as decent heroin, though that's way too much tylenol to be putting in your system, which is why people get upgraded to oxycotin if they actually need that much pain relief (in a very generalized way, percocet is basically the same as oxycotin, just a lot less of the main ingredient and with tylenol mixed in).
I've also met a fair amount of addicts/junkies in my life. There's a difference between 'junkie' and 'addict' in my mind, though. The only difference in my mind, is that addicts are well adjusted and/or smart, whereas junkies are idiots. Addicts will use all the time, but try to moderate the high so they can function when they need to. I used to be one (for pain pills, due to back problems, eventually got tired of it, off them now). Junkies just don't even give a shit, and will do some of the dumbest stuff possible chasing their high. Really, I have junkies to thank for getting me to want to quit taking opiates for my pain. I saw how fucking stupid they all were, became afraid I'd eventually go down that road/tired of being associated with them, and decided there had to be a different solution.