You also have the dreaded IS NULL OR construct (Q.ContactID = 15 OR @Orgid is NULL). Go to Gail's site, http://sqlinthewild.co.za/, and click the top Popular Link, Catch-All Queries, and read up.
Best,
Kevin G. Boles
SQL Server Consultant
SQL MVP 2007-2012
TheSQLGuru on googles mail service