No problem for visiting Americans (although I wouldn't recommend putting up an autographed picture of George Bush in the main saloon). I am not going to get into politics, but can tell you that I have been on Margarita Island for 3 months out of the last 15 and have met numerous Americans who will confirm that the locals hold no animosity towards Americans. They do hold a grudge against Bush,however, who they perceive (with some sound reason and international support) for having had the CIA finance the coup attempt against Chavez in 2002.
That being said, in Cruising World magazine, I believe it was the January 2007 issue although I do not have it at hand, there is an article by an American couple on 'Cruising the Islands off the Coast of Venezuela'. They indicated that it was not only their favorite cruising grounds in all of the Caribbean
, but also that they sensed none of the simmering animosity that they experienced in so many of the other large islands.
There are some issues with respect to crime (although the worst seem to be off Robledal, a beautiful yet isolated anchorage on the undeveloped side of the island). I have read nothing similar about Los Roques and, when one considers the huge number of yachts anchored at any one time in Porlamar, very few there as well.