The current stable version of this plugin is 1.1. If you download it through the WordPress repo you will get version 1.1. However, there is a new beta version 1.2 that you can use and test if you choose. Version 1.2 adds notifications for topic replies and well as some minor fixes.
If you would like to try 1.2 you can grab it from trunk (plugin repo) or download it from GitHub - https://github.com/jaredatch/bbPress-New-Topic-Notifications/zipball/master
If you download 1.2, please report any errors **or** any success here in the support forums.
1.2 should be fairly stable, however I have not had enough people test it for me to push it out to everyone.