Exchange 2010 SP2 is expected to be released by Microsoft second half of 2011. With the release of SP2 the way GAL segmentation will work has been changed.
GAL segmentation allowed administrators to optimize address lists in large companies, creating smaller 'virtual' organizations, with users only able to see the users they need to see.
In previous versions of Exchange GAL Segmentation was ACL based on a permission structure.
With Exchange 2010 SP2 GAL Segmentation will be delivered using an "Address Book Policy" assignment model.
Microsoft's intended audiences for this feature are organizations that:
- Require some form of sub-divided address book or who wish to create several 'virtual' organizations within a single Exchange Organization.
- Enable users to share some resources between these segmented user populations
- Seek to control which objects are visible to a user when they open their address book picker.
I will post more information on the new GAL Segmentation feature when given the thumbs up from Microsoft.