I have not been to Cuba, but can tell you that many people push to Key West or the Tortugas (preferably the Tortugas), overnight there, then punch across. If I am not mistaken, from the Tortugas to Cuba is only 60-61 miles... so it is closer than the mainland of the US.
If you are a US Citizen, I would probably not make that run while Bush is in office. The immigration is very lax in Fort Myers ( I have only seen a Customs boat there once), but I have been warned the US tracks boats in and out of Cuba. I do not know if it is true.
It is really a crock. I do not see the point of an embargo against a country when the rest of the world does not follow suit. Either get the rest of the world involved or try another avenue... but enough of my political chat.
PS The tortugas are beautiful and worth the stop. Better than Key West if you like beauty and seclusion... but I guess you would miss CatMan if you don't go to Key West!