Re the thumb UP/DOWN : I think that YEDDA should monitor the thumb up/down and "see" if they are "real" I.E. grades the answers or are given to change the statistics.
Another idea is to add a reason to why grade an answer with a thumb down. Is the answer wrong , the link not valid or the question was not understood?
I wrote also a detailed private letter to Yaniv about the subject but everyone can check my idea looking , for example on questions I answered yesterday 8.11 and try to decide if every one of them was so bad to get 4 thumb down...
I wrote that it would be interesting to find IF the same participants gave the thumb up/down or not.