Gerry McGovern makes the case against the "Rate my website" approach to appraisal. He is of course pushing an alternative too (which is well worth investigating).
I've used McGovern's style of survey to good effect (particularly in the support service side of things at the University) so can certainly vouch for his approach. I find it particularly effective when married with web stats analysis.
If you're new to his approach, his article is worth a read, and the free online seminar on 10 November I'm sure will be a great introduction.
Old Survey Methods are Broken - article by Gerry McGovern
Book to view the free online seminar on 10 November
Results of my surveys, inspired by Gerry McGovern's approach (you'll need a University username and password)