If you have systems that are still on SQL Server 2000 and that you are preparing for SQL Server 2005, run the Upgrade Avisor for SQL Server 2008 as well.  So, while you are under the hood of your database and app getting it ready for 2005, get it ready for 2008 too.  There are a lot of new features in 2008, but nothing that was taken away in 2005 and then reinstated in 2008 that would affect operation of the DB.  Many organizations have a policy that they wait until SP1 before implementation of a "new" product.  While the merits of that policy may be debtaed, you'll be one step ahead in your upgrade plans for SQL Server 2008.