Ask HN: Retargeting – does it really work?

I'd love to hear your success (or lack thereof) with retargeting.

Have you concluded that it delivers a positive ROI, eg are you sure those people weren't going to buy anyways?

My experience so far has been that it does drive sales, but that: 1. The number of clicks back to my site seems to be tiny and doesn't affect my bottom line much at all 2. Its hard to know for sure that I can attribute increase sales to retargeting (vs other campaigns)