See this article.

http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2007/11/07/MNIST7NS9.DTL

Granted today this data gathering focus toward this hobby is low priority to L.E. ; However given the ever increasing computer capacities, storage abilities,analysis software and marriage of surveillance technologies a few year from now you might get J-walking ticket in the mail showing a photo of you crossing the street to visit your neighbor.

Just recently read another article in which SJPD busted a suspected rapist by utilizing their new License plate scanning equipment that as they drive down the street it scans plates several hundred at a time...I am all for this in this case but story went on to mention other possible and likely application. Matching data with dmv records to know where and when you(car) is or track pace your (plates) to determine if your going 45 in a 50 mile street.

So not much we can do other than keep this in mind when on the internet making phone calls, and voting I suppose.