DBCC CHECKCONSTRAINTS WITH ALL_CONSTRAINTS won't actually make your constraints trusted. It will report any rows that violate the constraints. To actually make all of your constraints trusted, you can do the following:
DBCC CHECKCONSTRAINTS WITH ALL_CONSTRAINTS --This reports any data that violates constraints.
--This reports all constraints that are not trusted
SELECT OBJECT_NAME(parent_object_id) AS table_name, name
FROM sys.check_constraints
WHERE is_not_trusted = 1
UNION ALL
SELECT OBJECT_NAME(parent_object_id) AS table_name, name
FROM sys.foreign_keys
WHERE is_not_trusted = 1
ORDER BY table_name
--This makes all constraints trusted - but first anything reported by DBCC CHECKCONSTRAINTS WITH ALL_CONSTRAINTS
--must be fixed.
exec sp_msforeachtable 'ALTER TABLE ? WITH CHECK CHECK CONSTRAINT all'
Note that on the last statement, the WITH CHECK CHECK is not a typo. The "WITH CHECK" will check all table data to ensure there are not violations, and will make the constraint trusted, while the check will make sure the constraints is enabled.
See also:
http://sqlblog.com/blogs/tibor_karaszi/archive/2008/01/12/non-trusted-constraints.aspx
http://sqlblog.com/blogs/tibor_karaszi/archive/2008/01/12/non-trusted-constraints-and-performance.aspx