Great post providing information heretofore not seen on this branch.
Re foreigners traveling in a personal car, Poster #12 (Lackemacke) has it right. The law does not make it illegal simply to transport a foreigner in your car, but as in most countries, it is illegal to hire yourself out as a taxi unless you are licenced to do so. The big difference is that in most countries, simply having a stranger/foreigner in your car would not be presumed to be a commercial deal. In Cuba, it is presumed to be commercial, and the fact that the foreigner is in your car is all the "proof" needed that the owner is hiring his car out. While some drivers can talk their way out of fines, many cannot. A car I was once traveling in was fined US $90, the owner given 30 days to pay, or the car would be confiscated. (This was I think in 2001.) Not long ago, Truetown (a Havana resident) posted that hardly any private car owner in Vinales will now transport a foreigner because of increasing vigilance by the police in spotting unlicenced vehicles transporting tourists. I expect that, as with unlicenced casas, the law is more enforced in heavily-touristed areas than out-of-the-way places or on a busy Havana street.
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The same thing happened in Havana, the same year. I think it was late 2002. All of a sudden, the collectivos wouldn't pick me up and it was HARD finding a gypsy cab. One of the gypsy taxi drivers explained that they were confiscating collectives on the spot (no fines) if there was a foreigner found in it.
Pro tip