The FTC just released its Guides Concerning the Use of Endorsements and Testimonials in Advertising, and if you blog or are involved in social media and ever make product review or testimonial, this is guide is must read for you.  The guidelines go into effect December 1, 2009 and outline disclosure requirements when you post about a product or service.

The Guide provides a large list of examples of scenarious in which you would or would not be required to disclose relationships with product or service provides.  Even in cases where you provide honest endorsement in which the product or service provider has no control over your content, you may still be required to disclose.   Failure to include proper disclosure can result in fines up to $11,000 per instance, so the rule here is, don't take chances.  Be sure to read the Guide and understand your responsibilities.  It's just 81 pages and could be well worth your time.

I believe disclosure when making endorsements is the ethical thing to do and support the intent of the Guide.  My personal feeling is that some of the requirements are subjective, so it's best to err on the side of caution.  Also, the Guide fails to tell how you should make your disclosure - it just tells when you should make a disclosure.  Another issue with the Guide is that it doesn't directly address your requirements for existing endorsements - are you required to check your entire history of reviews and testimonials to ensure the relationships have been properly disclosed?  For these reasons, a site-wide Disclosure Policy (similar to your site's privacy policy or terms of use) might be a good idea.  A good resource is DisclosurePolicy.org, which has a free policy generator, a great blog on the subject and additional information about blog disclosure -  (DISCLOSURE : I do not have any relationship with DisclosurePolicy.org, nor did I receive any compensation for making this endorsement). 

As of this posting, I don't have a disclosure policy, but it is definitely in my To Do list.

Also, if you've read the FTC Guide on Endorsements, I would love to hear your opinion.