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From SQL Server Performance]
It is a fact of life: SQL Server databases change homes. They move from one instance to another, from one version to the next, from old servers to new ones. They move around as an organizations data grows, applications are enhanced or new versions of the database software are released. If not anything else, servers become old and unreliable and databases eventually need to find a new home.
The article continues at
http://www.sql-server-performance.com/articles/dba/migrating_databases_checklist_part1_p1.aspx