Abandoned DNA, plain view doctrine, and invasion of privacy

[Matt]

So, I had this discussion about the concept of abandoned DNA with somebody some time ago, but the concept is still kicking around in my head so I figured I may as well get other people's thoughts.

How do you feel about the concept of abandoned DNA? about police using ALPR's (those license plate readers they talked about that take hundreds of pictures a second)?How do we balance new law enforcement technologies/ concepts with privacy? When can these tools cause an invasion of one's privacy? How does one protect themselves in an environment when the scope of things police can get away with "in pursuit of criminals" infringes so heavily on innocent people's regular daily activities?