Travel to Cuba is a violation of OFAC unless you have specific permission. It used to be a $100 fine if we discovered your travel to Cuba upon entry into the U.S. There was a questionaire as well.

o CUBA-RELATED TRAVEL TRANSACTIONS - Only persons whose travel transactions fall
into the categories discussed below may be authorized to spend money related to
travel to, from, or within Cuba.

http://www.treas.gov/offices/enforce...ascii/cuba.txt