I think personally WP can be great and I'm guessing if they get threshold/W9 to work properly then it could be fantastic. The main issue is that we don't know how well things will be implemented and how good they'll be cross platform.
When the do the release it better work flawlessly otherwise the tech journalist will eat them alive. If it comes to the ecosystem half baked then it will be a big turn off for anyone wanting to get into the OS. So to me W9/threshold is the turning point for WP and a lot is riding on it.
Saying that, this year so far has been hugely disappointing for WP on the whole and it hasn't got any better yet. We're still missing features on apps, we're still missing major apps and games and MS still releases better apps and more apps to the other OS before their own. They have a major PR problem and image problem to over come. Let's see if they can do it. I have my doubts.