Currently there are a couple of ways to offer WSS to customers in a shared configuration:

  • WSS as a single offer: Lately a guide to prepare WSS for hosted configurations was published. This document explains what are the different aspects to consider to enable an infrastructure for multitenancy. The following matrix summarizes pros/cons of this configuration: 

Pros

Cons

Simplified no. of servers are required focused on a single service

Can be offered for dedicated customers as well

To provision workspaces, it has to be a manual process or scripts are required for automation (there are some scripts available which can be integrated with an existing control panel)

As the no. of customers increases the administration of the service becomes more tedious and challenging to manage

Configuration of AD/environment to support multiple tenancy is applied manually

The guide can be obtained in the following location: http://office.microsoft.com/search/redir.aspx?AssetID=AM102157711033

  • WSS as part of HMC 4.0: If you already have HMC (Hosted Messaging and Collaboration), the core infrastructure can be used to leverage Sharepoint Services to the existing & new customers. Next you'll find a brief list of pros & cons.

Pros

Cons

There is a provisioning engine available for creation of workspaces

Supports large scale of customers

There is a tool to automate the configuration of the environment in order to support multiple tenancy

Large no. of servers is required to leverage all the features of the solution

All the resources are shared

For additional details on HMC & WSS, you can consult the following references:

http://www.microsoft.com/serviceproviders/solutions/hostedmessaging.mspx

http://www.microsoft.com/serviceproviders/solutions/hostedmessaging4sharepoint.mspx