Aperture 3.2.3 or later: Migrating MobileMe albums and photos to your Aperture library
MobileMe service was discontinued on June 30, 2012.
If Aperture has not yet migrated your photos from MobileMe, this dialog should appear the first time you run Aperture:
When you click OK, Aperture should create a "From MobileMe" folder in your source list and add the photos you published to MobileMe to a corresponding album in this folder. However, Aperture cannot download photos that are not already present in your library from MobileMe.