Look at the UK to see where this is leading too. They started off with corner cams, now they are using imaging technology to do facial recognition, even behavioural recognition (eg people loitering).
On one hand we want to use it to protect the innocent. On the other hand we are slipping down a dangerous path.
Information is power, and power corrupts.
People don't like having cookies in their browsers because they don't want people tracking their web surfing habits. Well how will you feel when the govt can track your movements, and how secure will that information be (look at the pretexting case with HP for example). Will you movement habits be sold to a PI, or maybe a marketing company, or your employer?
And I'm not talking futuristic stuff here, pluging cameras into a high performance facial recognition tied back to a facial database is what they're doing in the UK and some airports already.