Settings | Ads | Your Interests

It's really interesting to see the full scope of the interests FB has gathered over time. Some of them are pretty hilarious.

They have a seemingly huge ontology of every subject you could think of. If you methodically go through an remove every interest, the ads suddenly become very generic - stuff targeted to, say, age group and/or location. Since removing everything, and periodically clearing it all out, I generally only see stuff for things like real estate and car dealerships, which don't really mean much for me.