Thought I'd add a post about this now instead of waiting for my regular Friday blog post.
ForumNG is now available as an optional add-on for standard Moodle 1.9.
If you run a Moodle 1.9.x installation, please feel free to try it out. However, do bear in mind that this is a pilot version and is sort of halfway between testing (i.e. earlier versions have been tested but we changed a bunch of things since). Please install on a test server first, and do not use for any real work unless you've verified for yourself that it is good enough for your purposes.
If you do find bugs please report them via the Moodle bug tracker. There's a link to that in the modules & plug-ins entry above.