I've been toying around with ArcMap 10.1 and ArcGIS Online. I think it's a great ecosystem, but it lacks one fundamental feature: you can upload a map- or layer package from ArcMap (works great!), but you cannot add that uploaded package to a web map. To add your own data to a web map (without resorting to ArcGIS Server), you need to use shapefiles?! Come on, it's 2012! For people who don't have the resources to implement ArcGIS Server, it sure would be great if it were possible to create web maps from uploaded map- and layer packages.