If you were to enclose a "Customer Feedback" card with customer orders, what would you ask? What would you want to know, or what information would be most valuable to you?

Something I learned the hard way: don't ask specifics. The request often generates distracting feedback of its own, self-nullifying its worth. I generally just offer a tangental reason to get back in touch with me and the feedback comes more genuinely.

I wouldn't ask for specifics either, accept maybe did you receive your product in a timely manner, was service courteous etc. I would leave comments about the work itself up to the customer. Maybe, somehow have a line stating for them to clearly describe anything they disliked, but I don't know if you want that or not. I have found that feedback that I get from clients is normally very confusing. One lady kept saying that her picture was fuzzy, but after asking her many direct questions, I found that she wanted more contrast and saturation.