One of my most popular articles was the series about Shared Hosting with Exchange 2007. Although the article had (and still has) a couple of followers, as soon as Microsoft released official documentation, Configuring Virtual Organizations and Address List Segregation, my advice was to use the guidelines provided by the Redmond company.
With the release of Exchange Server 2010 SP1, multi-tenancy was officially supported, and Microsoft started releasing other technical documentation, like the one mentioned on this blog post: Building Microsoft Messaging and Collaboration Cloud Services.
BTW, there’s more yet to come regarding GAL seggregation, read all about it on the official Microsoft Exchange Team Blog: GAL Segmentation, Exchange Server 2010 and Address Book Policies.
The documents in this file are intended to provide system integrators and service providers with guidance for migrating from Microsoft Solution for Hosted and Messaging Collaboration (HMC) to Microsoft® Exchange 2010 SP1 in Hosting mode.
This file contains documents help you deploy and migrate to Exchange 2010 SP1, SharePoint 2010, and Office Communications Server 2007 R2, including information about how to leverage the Exchange 2010 SP1 multi-tenant model. These documents include detailed steps and sample scripts for migrating Active Directory objects, Mailbox, and SharePoint content from a Hosted Messaging and Collaboration 4.5 (Exchange 2007 and Windows® SharePoint Services) platform. You can also use these documents for non-HMC environments.