Microsoft does it: bing.com/maps
Google does it: google.com/maps
Yahoo does it: yahoo.com/maps
Mapquest does it: mapquest.com/maps
...you get the point
I think there should be a redirect to the current http://www.arcgis.com/home/webmap/viewer.html?useExisting=1
This pertains to the ease of access...it's minor, but important for ArcGIS to follow suit.
Nick