"Google Storage for Developers enabled support for sharing with groups, for greater control & flexibility over how you share your data. You can easily share your Google Storage data with groups of users as well as individuals. You can share with groups by adding one or more Google Groups to ACL of bucket or object. A group member can be anyone with a Google Account, and members can authenticate using either their Google Storage credentials or in an authenticated browser session," writes Google.
Here's what you can do with group sharing: Share data with an entire department or mailing list; Make data publicly readable, but editable only by a group within your company; Keep access controls consistent with current membership of team; Add or remove a user's access to shared data via single group membership change without having to change access control lists (ACLs) on all buckets and objects involved.
More Info: sharing with groups