Stage 2. Then men became Internet users and were allowed to give feedback on a 5-star basis. Internet users still have opinions and share them in form of "Comments".
Stage 3. Following, users had the possibility to give a thumb up OR a thumb down. Users can reply to comments or even re-post them in their own opinion-stream.
But wait, there is more. The evolution of feedback and rating systems is not limited to the progressive simplification of the tools and the user interface. It rather (and more importantly) concerns what data are collected and associated with the users' ratings.
The person who is rating content or items (the "rater") has become the center of the action. This is somehow counterintuitive, yet the most valuable information for the website has nothing to do with the items rated thereby. In fact, the most valuable information is that one concerning the "rater": its tastes, preferences, behavior, etc.
Therefore, it is key that such information is made as standard and accessible as possible. For this reason rating on one dimension ("Like" button) may work better and eliminates certain "noise" in users' behavior analysis. Hence, simplification is functional to enhance user-profiling and, eventually, to better target those users with relevant ads.
On the other hand, all kinds of feedback regarding content/items have become a very effective "bait" to incentivize interaction and attract traffic. This happens despite being common knowledge that on-line feedback and ratings are easily manipulated and often unreliable.
I believe we can start looking at feedback and ratings from a different perspective. In fact, I have the impression that their social significance has changed as they do not represent anymore a vehicle to convey opinions but rather a form of basic interaction to show an acknowledgment that something does exist. To the contrary, if there is no "Like" button underneath it, such thing cannot be part of the user's profile for advertising purposes. And, that somehow makes that piece of content invisible on the Internet.