Here's a nice recap from Computerworld published today.
ArcGIS Online organizational subscriptions cost $500 per year per user for a minimum of five users, including credits for CPU use, data storage and bandwidth, Dangermond said. The credits are designed to be enough for "normal" use, although not necessarily for a public site receiving a million visits a day, or storage of, say, satellite imagery for the planet, Dangermond said.
The per-user price drops to $200/year for a thousand users. Customers who already have an ESRI Enterprise License Agreement will receive ArcGIS Online subscriptions for unlimited users and credits for each user.
There's also a Q&A with Jack Dangermond (but you need to be an Insider, free registration).
There's also a "What's new in ArcGIS Online" from the ArcGIS Blog.
--- update 6/13/12 ----
Oh, I guess the launch is today.
Starting later today a new look and features for ArcGIS Online, including both personal and organizational accounts. A milestone for Esri.
--- original post 6/11/12 ---
Original headline: ArcGIS Online for Organizations to June 14?
An e-mail from Esri suggests so.
Your Personal Account Won't Go AwayWhen you go to arcgis.com starting on June 14, you will see a new look. We are spreading the word about the new ArcGIS Online subscriptions and the capabilities it gives organizations. However, your personal ArcGIS Online account won't go away, and you will be able to continue to access your account and all your content from the new page by clicking Sign In at the top right.