Jennifer Granick of EFF has a commentary on a recent decision out of Massachusetts discussed here previously.
The Supreme Court of Massachusetts recently held that officers may not place GPS tracking devices on cars without first getting a warrant. The case, Commonwealth v. Connolly, was decided under the state corollary to the Fourth Amendment, and its reasoning may influence pending GPS tracking cases, including United States v. Jones, where EFF is an amicus.
Read more on EFF.