Unless you want to get sued (http://www.extremetech.com/internet/91966-aol-spotify-gigaom-etsy-kissmetrics-sued-over-undeletable-tracking-cookies http://www.ext

Unless you want to get sued (http://www.extremetech.com/internet/91966-aol-spotify-gigaom-etsy-kissmetrics-sued-over-undeletable-tracking-cookies http://www.extremetech.com/internet/91966-aol-spotify-gigaom...), I would avoid doing this until the legal grey area surrounding non-cookie tracking is resolved. I suppose you might be able to get a user to "agree" to this if you have them agree to a ToS when they sign up, but even then I'm not too sure of that.