In modern times, many of the disputes over federalism have to do with how many "strings" the federal government can and should attach to the money it gives to the states. We can see this in, for example, debates over Medicaid and over the No Child Left Behind law.
In both cases, the federal government gives a great deal of aid to states. In both cases, it sets out many rules by which the states must play in order to get that money. By doing so, the federal government exerts tremendous power over areas that the states feel they should control. Because of this, the states have tried hard to get out of having to obey the rules set by the national government. This process is ongoing today as people like Governor Perry of Texas want waivers of Medicaid provisions and states like Utah consider opting out of federal funding to avoid having to follow NCLB.
@pohnpei397: Although the states are under restrictions of the federal government, they receive aid from the federal by accpting the restrictions. Wouldn't the states be benefited from that?
Can you give an example of a case that has to do with the Commerce Clause?