The 2.1 installers for Windows come with Mercurial 1.9. There has
been a lot of API churn between 1.8 and 1.9, and I expect many
extensions to be initially broken by Mercurial 1.9 if they have not
been keeping up with the nightly builds. So verify all of the
extensions you will use before deploying TortoiseHg 2.1 across a large
set of users.