Winter '12 Force.com Platform Release
Permission Sets

Permission sets are now generally available. A permission set is a collection of settings and permissions that give users access to various tools and functions. The settings and permissions in permission sets are also found in profiles, but permission sets extend users' functional access without changing their profiles. For example, to give users access to a custom object, create a permission set, enable the required permissions for the object, and assign the permission set to the users. You never have to change profiles, or create a profile for a single use case. While users can have only one profile, they can have multiple permission sets.

Instead of creating “one-off” profiles, you can use permission sets to grant additional permissions or other access to a user. Permission sets can represent a concept, like a user's job title, or more specific access settings, such as a set of tasks that a user needs to do, like deleting or transferring records.