I put this on I just read the comment about letting websites put in "negative keywords" for natural search.
I use negative keywords on PPC and would be willing to use the same for natural search if only google would ask.
I'm an education site and the word "reading" is a striking example. Reading has three contexts: astrology, literacy, and a city of Pennsylvania (and maybe another in the UK). Basically, about 60% of the searches with reading are for astrology, about 25% relate to literacy, and the rest to geography. There are a few for others like poetry reading or health readings.
Since we don't really want each others traffic, someone should create a negative meta.
I optimize for learning to read or reading for literacy purposes.