The Mobile Me service is now discontinued as of June 30. However, owners of Aperture 3.2.3 or later can still automatically migrate their albums and photos to their local Aperture library for a "limited time," the support note said.
Aperture is Apple's professional photo editing and management software. Unlike the consumer-level iPhoto, Aperture supports RAW formats, a wide range of editing tools, and a plug-in architecture.
Aperture will create new albums in a From MobileMe folder, using the MobileMe names. Items from other sources, such as photos uploaded to the account from other people, will be placed in a project named From MobileMe and with a From MobileMe keyword added to each photo.
There are some differences in handling depending on the version you have.
If you have Aperture 3.2.3 or 3.2.4, the above applies only to albums created in your Aperture MobileMe web account, not albums and photos you uploaded to MobileMe from iPhoto. Use iPhoto to migrate these photos back to your computer.
If you are using Aperture 3.3, all MobileMe albums are migrated to your photo library, regardless of whether you uploaded them from Aperture or iPhoto. You can access your photo library from either iPhoto or Aperture; see Aperture 3.3: Using a unified photo library with iPhoto and Aperture for more information.