Well, I'll tell you one way to not do it, which is to measure against user expectations without any sort of normalization or attempt to figure out what those expectations are. Take for example this survey from a hotel I stayed at this past weekend:
As it turns out, I was expecting quality... and I got it. But as I fill out the survey I can't help but feel dejected for the poor folks who find out that "oh... we only did as expected." You know, the "no-smile-no-frown face".
What would they prefer... that I was expecting it to be a bad experience, and so when it wasn't a bad experience I put "Better than expected"?
Now I don't mean to imply that finding out what users expected of your product or service is a bad thing - but to not also have some less subjective measures seems shortsighted and demoralizing.