As of December 1st 2009, the FTC is demanding that all Testimonials not only be provable, but be inline with what the results that the "average" person can expect to achieve.
In other words, they will no longer accept testimonials that have the attached verbiage saying anything like "Results may vary" or anything of the sort!
This puts a HUGE burden on the marketer to test the results and come up with a provable set of results that the FTC will accept as "Normal".
And they expect your results to be compiled by an "unbiased" third party, which then becomes cost prohibitive for most marketers.
In the end, it is probably more prudent and less costly to either eliminate testimonials from your sites, or use generic ones that make no outcome claims at all, and saying only such things as that the testimonialist likes your product and would recommend it to others who need it.
But even that can be tricky as the FTC has stated that only testimonials of those who are "CURRENTLY" using your product, can be used in that way.
This would seem to say that if you give your product to someone to test and they like it, but do not continue to use it, you must not use their testimonial, or take it down once they cease to use it.
Further more, if you use such testimonials, and even if that person continues to use your product, you must prominently divulge that you gave them the product for review purposes, as the FTC feels that their opinion might have been prejudiced by your having given it to them, and they want the reader to know it!
These new rules have already been controversial to say the least, and will most likely have to be worked out in a court of law in the near future, by someone who can afford to fight it!
But unless YOU want to be that person, it is our opinion that is would probably be wiser to just stay away from most testimonials, until it all comes out in the wash ;o)