<p>Does anybody know what hypothetical indexes are used for in sql server 2000?  I have a table with 15+ such indexes, but have no idea what they were created for.  Can they slow down deletes/inserts?</p>

Not sure about 2000, but in 2005 hypothetical indexes and database objects in general are objects created by
DTA (Database Tuning Advisor)
You can check if an index is hypothetical by running this query:
```
```
SELECT  *
FROM    sys.indexes
WHERE   is_hypothetical = 1
```
```
If you have given the tuning advisor good information on which to base it's indexing strategy, then I would say to generally trust its results, but if you should of course examine how it has allocated these before you trust it blindly. Every situation will be different.