All basemaps added from arcgis.com via ArcMap's "Add Basemap..." button should be combined into the same basemap layer.

[DerekSwingley]

Currently, using ArcGIS 10 (final), when using the "Add Basemap..." button, each basemap that is added results in a basemap layer in the TOC named "Basemap." It would improve the user experience if all basemaps added using the "Add Basemap..." button were combined into a single basemap layer.