OK this can be an amazing tool for Japanese learners!
It's basically a huge database containing words in their actual context of use. The interesting thing is that it contains texts from various sources (from 会議録 to ブログ and 雑誌).
when you search a word (even a word that normally wouldn't come out from a dictionary - like dialects) a list of sentences where the word is used comes out with a lot of interesting infos (the sex of the writer, the type of media, the year of publication).

It can be used as a source of 例文 and you can have an idea of the frequency of the word in the different context and situations.

http://www.kotonoha.gr.jp/shonagon/