It can be frustrating when a client calls up and reports that the system is going slow all of sudden "with no one else on the system."
After investigating the usual suspects that slow the system down, indexing issues are what can some to mind next.
Needle in a haystack I hear you say!
Well SQL Server 2005 and above very cleverly keeps track of what it considers missing indexes when detetmining query plans.
You can query the sys.dm_db_missing_index_details management view and there are others if you're interested here.
This is information is gathered for all databases since the last time the SQL Server instance was started. Querying sys.dm_db_missing_index_details will return details of missing instances for all databases in the instance your current database is in.
