The problem we have found with Pinterest is that it's great only for a limited scope of niches.
For other indutries, it's quite useless. For example, if you have a plumbing company, your target audiences just aren't on Pinterest.
Plus, we've found that it's rather hard to funnel Pinterest traffic down to a landing page or something.
We do have a Pinterest account and a number of boards that we maintain. There's been some activity there, but very little to make any significant impact on traffic, conversions or sales.