The E2 Team at Microsoft (Enterprise Engineering) has released a new whitepaper and build guide about how to share data between two CRM deployments or organizations. The release can be downloaded here.

From the description:
While using a single CRM instance is probably the simplest way to accommodate the data sharing needs within an organization, using multiple instances of Dynamics CRM may be preferable in a number of scenarios. This release includes two documents, a white paper and a build guide, focused on sharing data across multiple CRM organizations. The white paper provides an overview of the levels of integration available for sharing data across multiple Dynamics CRM organizations, together with details about the techniques that are used for integration at the Application and Data levels, which include Web Services, Web Services-based solutions, Filtered Views, and SQL Server Replication. The build guide explains how to configure the Microsoft Dynamics CRM 4.0 April 2009 VPC base image to enable data sharing between a Publisher organization and multiple Subscriber organizations. The configuration demonstrates how to use Microsoft Dynamics CRM to maintain referential integrity between multiple organizations by leveraging Microsoft SQL Server 2008 transactional replication.