I submitted a script to SQLServerCentral.com and it’s been published today. The script automatically re-trusts foreign keys or constraints. It will also report any that could not be re-trusted. Discussion about the script can be found here. I have post here about how your foreign keys and constraints might become untrusted and why it is important for performance that they are trusted.
Note that the script I submitted to SQLServerCentral.com is a nicer version of the script I give at the end of my post linked to above. The difference is that the version at SQLServerCentral.com will report out the names of any foreign keys / constraints that could not be re-enabled whereas my earlier version only reported a count.