Maybe whether venting is useful or not also depends on the relationship between you and the person you're venting to.
To a trusted best friend, who understands you, empathizes and generally will offer an ear and possibly some good perspective, I think venting is both safe and productive. It gets the edge off, it lets you breathe, and the very act of sharing our frustrations with someone reminds us that we're not alone.
But if you're venting, for instance, to an office mate about a boss, that's not as productive, and may haunt you later. If you're venting about your significant other in a hurtful or gossipy way, you won't feel very good afterward. Or if you're venting to someone who can't be trusted to keep your words to themselves, you're probably hurting more than helping yourself.
I'll tell my best friends just about anything, and it helps me to move on. But other than that, it may be better to just go to the gym and pound out that frustration in a workout. When the endorphins kick in, you'll be in a much better place.