The US relationship with Cuba has, for over a century, been marred by the relics of colonialism and totalitarianism. Without defending the totalitarianism imposed by the Castro regime at all, it wasn't substantially better (or worse) than the dictatorship of his right-wing-nutcase predecessors, or for that matter of Spanish colonialism. Each set of dictators had different emphases in their respective brands of repression, and in how they shared power with "middle management" of that sad island's affairs.
Fidel Castro's resignation does not mark the beginning of democracy in Cuba. Cuba has never had a democratic tradition; it has a long way to go before it can create one. And watching the politics ninety miles north of the island surely cannot be very inspirational.
Ironically, Castro's resignation has pushed news of an equally dangerous dictator's potential demise below the fold. The election results in Pakistan are in, and Musharref and his allies lost decisively at the polls. This might lead to a non-military government; I give it 36 months at the outside before the military steps back in, presuming that the military even allows this government to take power. Remember: Unlike Cuba, Pakistan is a nuclear power.