In addition to the Drupal 7 porting effort, this release contains all changes from the 6.x-1.x branch up to September 20, 2011.
Things to watch out for:
1) Make sure to take a backup of your site before attempting an upgrade! The update code has not been comprehensively tested and there are KNOWN bugs!
2) support_update_7002() attempts to migrate comment_upload data into a file.module field. Due to the way files in Drupal 7 are stored, and more stringent validation, it is possible that this update will fail. The two failures that have been found so far are:
a) If you have an extremely long filename, there may not be enough space to store the full filename in the table, and the update will fail.
b) If you have multiple files with the same case insensitive name, the system will not be able to store them both, and the update will fail.
If this turns out to be a common problem in practice, we will write code to attempt to work around these. If you hit either, please ask in the issue queue for assistance.
3) Access control may still be a little off. Please report any issues you have.
4) The query altering used by support.module is known to tickle a core bug regarding unqualified column names. If you suddenly have "column ... in where clause is ambiguous" errors appearing in other modules, please see #766382: Column 'nid' is ambiguous when using node access modules.