Tim,
Your last comment was really interesting; I read thru the tabs on the ArcGIS description link, you provided, and just took another look at the ArcGis.com map viewer. It sounds like you have access to a paid subscription of arcgis.com; I hope you won't mind if I ask you a follow up question, since I can only access the free subscription. You've helped me define my original question better. I'm interested in just the map viewer capabilities of the two, Explorer & arcgis.com, free subsription. My understanding is that both allow uploading a shp file with 1,000+ features. Is the buffer tool, you mentioned, and the geocoding service, mentioned in the description link you provided, available with only the paid subscription, since I can't find either of those features in the map viewer of my free subscription? I watched the ESRI webinar on arcgis.com and I'm still confused.
thanks for your patience helping me,
Ken