I love the "block" functionality, but it is really a different feature. Block says "this site is spam, don't show it to me anymore." "-1" says "this result isn't relevant to what I'm searching for, alter the future results accordingly."
Regardless, I love what Google is doing here in taking individual consideration into account.
This is good interpretation of the functionality is meant to be used.
However, we have seen several cases where the usage of the functionality slowly drives how the feature is morphed and I am guessing Google is experimenting with the button initially to see how the users like it and would try to weave other functionalities around it.
Regardless, I love what Google is doing here in taking individual consideration into account.