Thanks for the replies. I wasn't really thinking customers as much as other product publishers. If they are in the same niche they would have a great targeted list... so would they feel like you're are competition or be open to promoting your product.

I'm so close to launching right now that I decided to contact some of those in my niche about jv's and cross promotion. We'll see what happens, but even if some decided to compete and others decided to promote it would be a good situation.