There's nothing about the change in Blogger Buzz, but they've posted a long announcement in the current BHF, and linked to a Getting Started Guide which shows the base features of Google Product Forums, and an example working GPF-based forum (the one for Google Plus).
Key facts about the change:
- Posts from the current forum will not be moved into to the new forum (since most of them refer to the old Blogger interface).
- You will need to join Google Groups to use it.
- All user levels will reset to Level 1 (presuming not TCs though) - but if they look to make more TCs, your post-history in the old BHF will be checked.
- The only way to get a picture with your profile in the new forum is to have it linked to your Google + account. (I tested with an account that's not +'d, these do basic Google profiles that don't include pictures).
- The existing BHF will be archived, so the current content can still be found.
(Not sure what "archived" means - probably that write-access to it will be turned off, but read-only access will be continued).
- All help-links inside Blogger will go to the new forum, once it's live.
- The new forum will be at: https://groups.google.com/a/googleproductforums.com/forum/#!forum/blogger
One fantastic feature of the new forum is the keyboard shortcuts, eg "space" to move down a page. (Bringing back fond memories of the first use-net reader I ever met, back in the days of Vax VMS :-)