I have clients that are tempted to sign up for such services. I don't have any first hand experience using any of them, so I can't recommend either way.
I'm intrigued by the idea of being able to catch and address negative reviews before they find their way online.
Software like this (getfivestars dot com) has an interesting approach to filtering and addressing the negative feedback. I'm sure there are others like it.
Would love to hear some thoughts on this.