I know our clients get tired of hearing this, but I can't say it enough: social media is about networking and building relationships, not about broadcasting your own message incessantly. Nobody cares about you and your product. They care about how you can help them - whether it's solving a problem or just having fun.
A friend of mine is a good example: he followed a link in an email to read a story by an awesome artist whose work he admired, then reached out in the blog comments section saying he enjoyed the story. Then he tweeted the story to his followers. Guess what? The blogger followed him back after that, and ended up asking him to participate in a project he was doing. You just never know who you might meet through social media, just like you never know who you might meet at a party.
You wouldn't go into a party and just start talking about yourself, constantly interrupting others to tout your achievements, would you? At least I hope you wouldn't! You would engage in casual conversation and get to know people you have something in common with; over a period of time you may run into some of those people at other events, and may eventually get a referral or a sales inquiry from one of them. You don't NOT go to parties because you never get sales at them, do you? No, you go for camaraderie, fun, and enjoyment.
Just the fact that there's so much you can learn from other people is reason enough to use social media, regardless of whether you ever get a sales lead. Regardless of what your interests are, you can probably find others who share those interests and know things that you don't.
Stop talking and start listening!