Jerry Jeff Walker is probably the biggest "celebrity" to regularly visit San Pedro. Michael Jordon was there once, as was Mick Jagger. There probably will be more, given the popularity of "Temptation Island."
The stars of the "Dogs of War," "Mosquito Coast" and "Heart of Darkness" also spent some time in Belize, though mostly on the mainland rather than on the cayes.
Of course, the well-known Marty Casado also visits regularly.
The movie filming while you were there was a TV movie, "After the Storm," based on a Hemingway short story. Ambergris Caye, Belize City and Placencia stood in for the purported location, the Bahamas in the 1930s.
Belize First Magazine http://www.turq.com/belizefirst/