Genesis 1.9.2 was the second bug fix release for Genesis 1.9.0. It was expected to be the final release on the 1.9 branch before Genesis 2.0.0 is released.
Genesis 1.9.1 was a bug fix release for Genesis 1.9.0, that addressed an issue with the loading order of child theme style sheets.
Genesis Framework 1.9.0 is a major release and has a completely new front-end design, and some nice improvements for both developers and users.
Genesis Framework 1.8.2 is a minor release – a compatibility update for the recently released WordPress 3.4
This was a security release. Details of the issue are currently held back until users have had time to update.