The Changelog, taken directly from the development site, is shown below. The latest version you see may still be under development and there is also sometimes a delay between creating a new version and having it available for download on this website.
Generally speaking each version is back compatible with earlier ones, but every now and again the decision may be made to break back compatibility to make things better in the long run. For example in version 3.2.2 the name of a taxonomy was changed from 'Main Index Featured Image' to the more appropriate 'Slider Image' which meant the Slider Images had to be selected again, and in version 3.3.0 some variable names and sidebar IDs were made more meaningful which meant the widgets became inactive and had to be dropped back onto the sidebars.
Something seems to have happened to the tab stops as WordPress has updated and now the changelog doesn't format very nicely.