Eric Hansen and Lubor Kollar from Microsoft have a helpful article on TechNet that does a very good job of explaining how statistics work and are how they are used in SQL Server 2005. I previously posted some helpful statistics information here.
I’ve been fighting my own battle with SQL Server 2005 statistics on a particular table on one of the databases that I support. This particular table has about 14 million rows of data (which is not that large), but it is extremely volatile, since about 5-6 million rows are inserted and deleted from it every day. At any rate, I will talk more about this in the future.