Matt,
Just launched a new site in DNN 9.1:
http://www.mdrealtor.org/
I think the better question is "Is it feature complete".
Most of the gripes you will hear is about the Persona Bar and the admin modules.
I get where they are going with the new Persona Bar. It is faster loading but not all the admin tools have a 1to1 counterpart in DNN 9 yet.
Page Management / Page Settings are still a mess. And the Site Settings screen is also lacking.
Top things that bug me right now:
1. I cant create a page that links to a file and upload the file at the same time unless I dump it in root.
2. I cant link to a page that is a subpage of a disabled one.
3.Cant add a module from another page that is a subpage of a disabled one.
4. No persistent edit mode, no layout mode, no way to switch out of edit mode without logging out.
Michael