We've been serving business customers for almost 4 years. Most of our customers are getting anonymous comments from their customers, but you can use the same technology in your office environment.
If you want to take the pulse about what your employees are thinking, and get their honest opinions, use TalkToTheManager.
We provide you with a phone number that you display in your common office areas (the break room, water cooler, etc) and all your employees have to do is send a text message.
We forward the messages to the management personnel that you specify, and all employee phone numbers are hidden.
If you need to reply to an employee, just reply by text message or email, and they won't see your phone number or email, either.
You'll get both the good and bad about your workplace, and can work to make it great for your employees. Let them know you're listening and want to make things better, and you'll have more loyal employees who take pride in their work.