Depends on many factors, your content, your placement, how web savvy the visitors are, where visitors come from, what kind of content is your site, using galleries and thumbs or gateway. It's really very open - I had a month of 6000+ installs for a lousy $60 - because traffic was vietnam and china mostly.
It depends on a lot of things as the user above said. I've noticed that traffic from search engines performs better than traffic from referring sites. Also, the content must "force" the visitor to install ZangoCash, in other words, people should want to view your content (that's why porn video sites work so well with ZangoCash ).