I took the new management interface for a spin with MacStories, and it looks great. Clean, responsive, faster than ever. The people who worked on Calypso clearly put a lot of thought and willingness to start fresh into this.
As for existing WordPress users (both .com and self-hosted versions):
If you’re an existing WordPress.com user, you already are! Elements of the new WordPress.com have been progressively launched over the past eighteen months. If you run your own self-hosted WordPress site, you can install the Jetpack plugin to use the Calypso-based editing and management tools. Your site will be ready to go once you log in to WordPress.com.
A new Mac app has been released to manage all WordPress sites on the desktop, and Automattic told me the mobile apps have already been built on this backend as well.
Last, make sure to check out Matt Mullenweg (CEO of Automattic) on today's launch and decision to go open source:
This is a beginning, not an ending. (1.0 is the loneliest.) Better things are yet to come, as all of you dig in.
WordPress is such a great success story. I'm very happy I chose to use it over six years ago.