This document will outline things that need to be noted when upgrading your installation from 1.x to 2.0.
Facebook accounts will be de-authorized when upgrading to 2.0. This is because Social now requires the offline access permission. Any posts broadcasted to your Facebook accounts will not be aggregated until you reauthorize your Facebook accounts.
If you used a custom comments template via the SOCIAL_COMMENTS_FILE constant, please be aware that the following changes have been made to how the comments are displayed.
In 1.x to display the comment form you would call Social_Comment_Form::as_html(); now you must call echo Social_Comment_Form::instance($post_id);