I’ve gotten this question from a couple of people (mostly probably because they want to see me say Google Earth Killer).
Lets get this out there right now. ArcGIS Explorer (AGX) isn’t ESRI’s answer to Google Earth. The reasons for AGX are tied very closely with ArcGIS Server (AGS). AGS needed a client application and since you can have globe services, AGX needed to be a digital earth application. That said, Google Earth has influenced the direction of AGX since GE became a household name. To create a digital earth application and not have it compatible with GE is not a good idea and ESRI has done their best to accomplish this. They also seem to have learned from the community and are supplying maps for users to use even if they don’t have a AGS to connect to. Personally I think both tools will sit on most peoples desk (at least those who can run GE legally). From a aerial photo standpoint, nothing will compete with GE out of the box. But the hope is AGX can allow users who want to combine data layers beyond KML on their client a way to do so as WMS, ArcWeb, ArcIMS, ArcGIS Server, Shapefiles, Geodatabases, KML and rasters are all supported.
If you want to know if AGX will be a Google Earth killer, then you aren’t asking the right question. The question is how will any of these digital earth applications (Google Earth, NASA World Wind or ESRI ArcGIS Explorer) help me get my tasks done better. The answer to that question is probably different almost every time you ask it which is why you need to make sure you understand how all three will help you work smarter.