Notice that the pattern becomes problematic when you include facebook in the picture, because that's where people give away their real data. I don't think it's

Notice that the pattern becomes problematic when you include facebook in the picture, because that's where people give away their real data. I don't think it's an issue with UDIDs - they are an essential component with minimal privacy implications in itself. The problem is mostly with facebook's weak privacy tactics. There is no privacy setting that can hide your fb uid, and indeed, facebook has been very lax about giving it away to just about anyone.