Unfortunately we cannot go into too much detail about what's new in the next release of ArcGIS Explorer (1500) - http://blogs.esri.com/Info/blogs/arcgisexplorerblog/archive/2010/05/19/a-virtual-city-look-ahead-arc.... However what we've been focussing on is fixing as many as possible of the issues people have reported using 1200 plus working on sharing content and integration with ArcGIS 10 and ArcGIS.com. It's a really exciting release and should be available shortly after ArcGIS 10 is released.