Microsoft have released details of a new feature available in SQL Server 2005
Enterprise Edition:
Scalable Shared Databases.

What is it?

A read-only database stored on a SAN than can be attached to multiple SQL
Server instances. It will allow you to have multiple instances of SQL Server
host the same database, with the same results guaranteed, so that you can scale
up the number of SQL Servers without having to duplicate the database files.

As database design progresses towards even larger databases with reporting,
web service and OLAP requirements this feature will help with scaling load on
SQL Server instances, without adding to storage costs. If currently you have a
dedicated instance of SQL Server for each of these requirements you would also
have a dedicated copy of the database files. With Scalable Shared Databases you
would only have one copy of the files.

More details on Scalable Shared Databases will be released with a Books
Online update expected in December.