For the most part, I don't collect anyone's data. I do, however, utilize the ol' google analytics on my site because I'm curious about how my site is access, where from, etc. and I'm also curious as to how I can make my site more findable on the web.
The above is the fundamental dichotomy posed by search engines that are text/semantic data based and being someone that works mostly in the visual/non-textual realm.
Past that, however, I really don't want to know or keep tabs on you. If you stick around and become my friend that's different but, then again, that's not a typical web surfer/website relationship.
If you follow me on facebook or twitter or whatever, I believe that gives me access to certain amounts of data. Which, again, I'm not concerned with and make no effort to keep. I'm not too sure what to make of the fact that (according to facebook) 51% of my fans are women while <49% are other. I guess that's good? Or is that bad? Gender doesn't concern me. Nor does your race, religion, pant size, etc. I'm tired of that game.
With that said, if you buy something from me I will, of course, need your contact information and an address. I may hang on to that but, chances are, it'll be written on an old napkin while I make a shipping label and then immediately lost/thrown away/used--thereby rendering my data retention scheme useless. In short, if you buy something else from me you'll probably have to reenter your data.