I never knew anybody who went to jail for speaking against the government neither directly heard such a story but I can believe that happens(journalist Yoanis Sanchez is an example). This is the way I see it, the government normally don't care much about this people or what they think/say, except when they try to do something that could affect their public image, for example if the Pope comes to visit and they want to organize a public protest. In this circunstances they are preventively sent to jail, and afterwards released when the visitor is gone. It is often the case that real criminals present themselves as "politic prisoners", that adds much noise to the whole situation and usually gets exaggerated by the media in Miami. While this is not ok, in Russia people actually get killed in similar circumstances, while the main opposition leaders in Cuba are all alive.