What are the legal consequences for doing mushrooms?

For specific consequences, look into the laws governing where you are. 

Per Erowid:

"Psilocybin mushrooms are not specifically named in the U.S. federal scheduling system, however their two primary active chemicals Psilocybin and Psilocin are both Schedule I in the United States. This means they are illegal to manufacture, buy, possess, or distribute (sell, trade or give) without a DEA license. Fresh and dried psilocybin mushrooms are considered containers of Psilocybin and Psilocin, making them illegal to possess as well."

As for US state law, psilocybin mushrooms are illegal to possess in every state except Florida, punishment varies depending on the state and circumstances of arrest.

For more information on Psilocybin Mushroom laws check out Erowid's vault at http://www.erowid.org/plants/mushrooms/mushrooms_law.shtml