Went to Cuba a few years ago - no prob at all but in RIBs you will have to look out for authorities - make sure you land at a proper port.
Very good article here - read it all - US boaters need permission from USCG for example.
http://www.southwindssailing.com/art...208/cuba2.html
Just remember the people are very poor so try not to flash any wealth around when walking the streets - common sense really.