A couple people have commented recently about this blog or via twitter about the possibility of ArcGIS and the Cloud. The current licensing of ArcGIS Server pretty much precludes the possibility of running it in the cloud so until ESRI changes the licensing or works with a company to provide ArcGIS Server in the cloud don’t get your hopes up.
I’m guessing it is virtually impossible for ESRI to license ArcGIS Server in the cloud as the product stands today.