This article discusses the use of GPS trackers by police. Basically, the question is whether police should be allowed to put GPS trackers on suspects' cars without a warrant.
If you take the position that there's nothing wrong with giving the police a little more power in order to better find criminals, which is a perfectly defensible position, then there seems to be little wrong with this approach.
If you have strong libertarian tendencies, then you might find this law alarming. After all, it opens up possibilities for large-scale surveillance (although cellphones already do this somewhat), and could definitely be used for political ends -- before the prostitution scandal Spitzer was already embroiled in a controversy about tracking Bruno, his main opponent.
Personally, I think that warrants should be required, since there is not a very strong case for warrantless tracking. The law on search and seizure requires investigators to get a warrant from a judge except in cases where urgency is required. There are very few situations I can imagine where warrantless GPS trackers would be necessary. Tracking with warrants is a valuable tool, and may find more use in police forces around the country.