There is a huge overlap of functionality between ArcGIS Explorer, ArcGIS Explorer Online, and ArcGIS Online. Each has a limitation that is addressed by the other product. Granted they are intended for different functions, they are basically attempting to accomplish the same mission. The biggest limitation is that ArcGIS Explorer provides 3-D functionality, ArcGIS Explorer Online and ArcGIS Online do not. Google Earth is on the web in 3-D imbeddable in web pages. Esri does not yet have the 3-D capability on the web. Silverlight limitation? Second, ArcGIS Explorer and ArcGIS Portal can be deployed within an enterprise, whereas ArcGIS Explorer Online cannot. ArcGIS Explorer Online is a web based version of the desktop application, whereas ArcGIS Online and Portal are all web based. ArcGIS Explorer and ArcGIS Explorer Online provide presentation/visualization, but how is this really different than an ArcGIS Online map or an ArcPortal template? I think there is a tremendous opportunity to consolidate these solutions into one. The missing component is 3-D visualization. This would provide scalable deployments as one product. 1) on the desktop client 2) within an enterprise as a web portal application 3) in the public/hosted/crowdsourcing arena. It would provide rapid deployment and support methodologies. At present we need to develop config files for Explorer, which would be different than map templates, or Portal, etc. - all different means to deploy/support! This would bring ArcGIS closer to the "consumer" or non-IT user market such as Google has with embeddable API/code. (PS - Seamless integration with SharePoint would be great too and what happens when Silverlight changes with HTML 5).