The (not so) simple answer is that it really depends on your business practices and, yes, of the product you are trying to sell.
If you are a startup, trying to get the word about your business out, I think it can be extremely effective. People will see it and, if you are original, they will start talking about it.
But, as I always defend, you have to be original, you must have a great product. If you are a startup and your product sucks, quit. No kind way of saying it. But if you bring real value to the table, Facebook is indeed a great way to expand knowledge about your brand.
However, if you are a big company forget it. People already know about you. People are sick of knowing about you, they will either buy from you or not, and Facebook is not going to change that. The only reason to be on Facebook as a big company is to spark conversations and get real feedback, and ads don’t fit that role.