There’s a great article about how to ask your clients for effective testimonials, ones that aren’t too sugary, ones that can speak to the real needs of your customers over on the Psychotactics site.
Ask the client three questions:
1) What were your perceptions before you bought our product/service and were you reluctant in any way?
2) How did you feel as a result of using the product/service?
3) What specific results did you get as a result of using the product/service?
For more information read the complete article, it explains how you can avoid getting testimonials that are ineffective and too flowery or vague.
The Psychotactic website says it "unlocks the mystery of the business brain"…good luck on that one.