I have a site I'm going to create, which is a free service for folks (and for myself, the main reason I want to build the site). But since I have this hypothetical site, and folks will hypothetically be entering content, I would like to toss Google AdSense on to make a couple of, er, cents.

However, this is not data that all users would be comfortable with being made public, I think.

Any suggestions on how to get good targeted keywords despite that?

The only thing I've got at the moment is jumbling all the data for a given page, picking out relatively uncommon words, repeating them a bit, and serving that up as stew for anyone who isn't the owner of the data to see.