With ArcGIS Online, you can quickly create interactive maps and custom apps, and then publish and share them in Esri's secure cloud. You can share content through groups with members of your organization, keep it private, or make it public. You stay in control of your data, lower your IT costs, and empower your users and customers with easy-to-use, web-enabled content. Organizations will be able to evaluate and purchase a subscription for an ArcGIS Online organizational account in Q2 2012.
EvaluateThrough a subscription, you get flexible data storage capabilities and administrative controls for managing user roles and access levels. You'll be able to invite specific users or groups of users with already established logins used in your organization and monitor usage through an intuitive dashboard.
Read the ArcNews article Tailor ArcGIS Online to Your Organization or watch a short video to learn more.
These can be accessed by web, desktop, and mobile applications anywhere through the internet. You can choose to share these hosted services with everyone or keep them private.

Add your logo and banner, create a custom URL, and display maps that are important to your organization and your users in the Map Gallery and Featured Maps sections.
Access content published by Esri and GIS users around the world to make your own maps, or create mashups with the built-in map viewer. You also get unrestricted use of ArcGIS Web Mapping APIs to build custom web applications, and or use one of the configurable templates to quickly create a web mapping application or embed your maps in blogs and websites.

To learn more about making web maps, read: Intelligent Web Maps and ArcGIS Online (ArcNews, Summer 2011)
Share maps and other information using groups, where you can communicate information, designs, and other ideas. You can also create destinations for your users and customers with ready-to-use templates. You can share your information publicly, or keep it private.
To learn more about sharing maps, read: New Map Template Provides Fast Access to Web Maps (ArcNews, Winter 2011/2012)