I have an app and am looking to promote it.. I was thinking whether anyone would be open to allowing me to use their app's user data (not see it, just use it) to promote my app to those users. I am looking for users in certain demographics and with certain tastes. Will give details if there is interest.

Has anyone tried to do this in the past? Did it work? Challenges?

Thanks in advance.

Sure you can promote your app inside another one, I think AdMob is really what you are looking for expecially if you wanna target to user with those kind of interests/characteristics.

You could also give developers you know a banner or a thing like that, but it could be difficult to target.
I mean, eg, we got PhoneInfo (free app) on the market and we could add a banner from you, but we should take an agreement and perhaps users would not be so happy to have a part of the screen showing something which is really not related to PhoneInfo or gsm/wifi stuffs...