Just some input
I think I agree with whoever wrote surveys might not be as objective, I think that measuring other things are much more usefull like carreer possibilities, abcense, but also efficiency trends, an unhappy employee will work less fast, so if you have an employee with normal 98%efficiency performance dropping down to 80% on the same process, you know that something is wrong, doesn't necessary mean that he/she is having difficulties at work but it could be an indication.
but still if you want to know your satisfaction internally, you will just have to spent time with the people, it might not get you your desired measurement but for improving your numbers it is a great tool.