Dynamics CRM version 4.0 adds a number of new features, including support for duplicate data detection and other enhancements. Perhaps most importantly, CRM 4.0 provides true multi-tenancy, which will allow the creation of multiple organizations on a single server. CRM 4.0 was released with the following improvements:
New in Microsoft Dynamics CRM 4.0 are readonly licenses. Users that do not have to have write permissions can be assigned Read Only licenses. These licenses are cheaper because they do not allow any write operations on the records. If later a user should be able to perform a write operation, a step-up license can be bought to upgrade the Read-Only license to a Full Client Access License.
Full Use Licenses are licenses where the client (user / device) has read, write and update permissions.
Whenever an application (windows or web) reads or writes data from/in Microsoft Dynamics CRM, an external connector license is required. External Connector licenses are only valid when bought for a Professional or Enterprise edition. It is not allowed to use them with a Workgroup Edition.