Reto Meier noticed that Google now is allowing users to rate posts in Google Groups.
At this point, it isn't clear for what purpose the ratings will be used. In the long-term, I could imagine that they might allow them to filter out spam and crap, filter in the best posts (like Slashdot), or even recommend articles based on what you tend to like.
If you're interested in this kind of thing, there is some fun previous work here. Don't miss the old U of Minnesota paper "GroupLens: Applying Collaborative Filtering to Usenet News". And I really enjoyed the paper "Slash(dot) and Burn" by Cliff Lampe and Paul Resnick.
When looking at this, I also noticed that the Google Groups home page now makes group recommendations, a list of "Suggested groups". I'm not sure what information Google uses for this, but I was amused and a little taken aback to see that my top recommendation was alt.support.cancer.prostate. Does Google know something I don't know?
[Found via Philipp Lenssen]