Don't aggravate customers with annoying surveys!
Make sure to ask "Is there anything else?"
Several stories about bad feedback forms
Interviewing 5-10 customers is probably as good as interviewing hundreds
Don't assume that no complaints = customer satisfaction. They may just be putting up with it, especially if they feel no one is listening.
Don't just do surveys. Use different feedback-gathering methods. Invite open-ended feedback, in surveys or otherwise.
Don't ignore the feedback!
Focus on the service attributes most important to your clients. Don't know what's important to them? Better find out!
"What aspect of our service is most important to you? Regarding it, how are we doing?"
Lots and lots of examples of how not to
FBWA (Feedback By Walking Around)
I love how Microsoft gets all Ajaxy with feedback on every page: http://msdn2.microsoft.com/en-us/library/ms229931.aspx
Again, act on the feedback! Summary of responses, detailed responses, action
Don't forget power of the naked eye. Often problems are obvious and don't need surveys