I'm trying to find an answer to this but haven't been able to so far. I'm looking at a certain long tail keyword, and one site ranks on the first page when the keyword is put into quotation marks, but does not rank on the first page when quotation marks are not used. Why is this?
When you search in quotes you get an idea of the competition for you keyword. You should notice that the results that google shows are much less when you search in quotes than when you do a straight search. So this would say to me that google has indexed your page for you long tail keyword...that's good...now you just need to get some backlinks to that page with your keyword as anchor text to move up the ranks in the straight search. Hope that helps...
This happen because whenever you search with quotation mark Google will give only results that matches with the quoted keyword.