Are there specific examples you have in mind?



Yes...over half the states in the U.S. are suing the federal govt over mandated health care:
http://washingtonexaminer.com/blogs/beltway-confidential/2011/01/half-states-now-suing-federal-government-over-obamacare


Five states have introduced legislation to nullify any proposed federal emissions regulation under the "cap-and-trade" model

There are also a host of state sovereignty resolutions and state sovereignty bills in about 30 states. While a few don't have much merit, a number of them do.