Landorus is apparently now Ubers, and Froslass is OU. What were the others and when did this happen?
I don't know about Landorus, but if you go to the Smogon home page, there is a news item about Froslass, and its dated the 17th of Aug, so I assume that one happened then.
Look here for the page I was talking about.
EDIT: Also on the same news article it mentions Snow Warning was banned from RU, just to answer the second part of your question, even though this isn't really a complete answer.