If I really like a drama that just started airing, I'll rate it immediately and change it as it airs. But, it definitely doesn't make sense that people are able to rate dramas that haven't even aired yet! I've seen this with not only dramas but movies as well: http://mydramalist.com/17279-fullmetal-alchemist
And, Black was rated 1.0 by somebody (who probably hates it very much already): http://mydramalist.com/23772-black