What are the US Customs requirements upon returning to the US after pre-clearing customs in the US Virgin Islands?
You're required to notify and clear customs if you land in the 50 U.S. states or Puerto Rico from the U.S. Virgin Islands, even though the U.S. Virgin Islands is part of the U.S.

"All private aircraft arriving in the United States via the Gulf of Mexico or the Atlantic
Coast from a foreign location in the Western Hemisphere south of 30 degrees north
latitude, or from any place in Mexico or from the U.S. Virgin Islands, shall also furnish a
notice of intended arrival. Such aircraft must then land for inspection at the nearest
designated airport unless an overflight exemption has been granted under Section
122.25 of the Customs Regulations."