I haven't seen this discussed - maybe someone here has. The Fact Sheet put out by the American Celiac Disease Alliance, regarding the new Food Allergen Labeling and Consumer Protection Act, says:

How Can I Determine if A Product Is Gluten-Free?
Step 1
Is wheat in the ingredients list or is it listed in an allergen statement beneath the ingredients list? If Yes, Stop! This product is not gluten-free.
If No, Proceed to Step 2.
Step 2
Read the ingredients list. Is there Barley, Rye or Malt listed?*
If Yes, Stop! This product is not gluten-free.
If No, This product is gluten-free and safe to eat.
* People with celaic disease are advised to consult with their physician about including oats in their diet.

My question is, what about hidden barley or rye (or oats)? Are there no ingredients that are derived from these grains? I sent an e-mail with this question to the ACDA, and received no response.