If you run an UPDATE statement on the partitioning column of a partitioned view and the UPDATE statement includes an inner join to another table, SQL Server might perform a scan of each partition table. This problem occurs even if a useful index exists on each table. Depending on the size of each partition table, scanning each partition table can negatively, and sometimes severely, effect performance. Read the Microsoft article "FIX: A scan of each partition table may be performed when you run an UPDATE statement on the partitioning column of a partitioned view" at
http://support.microsoft.com/?kbid=813146