In April of this year Google released an update to their search algorithm which decides where your site will be ranked on Google. This update was to filter any websites that Google saw as spam and give higher rankings to more credible websites.
This is a great update by Google allowing sites like yours to receive higher Google rankings.
Now Google has released a further update, Penguin 1.1 to filter out any websites that were missed at the initial launch. Though this will unlikely affect you (it will actually only affect <0.1% of searches) it is worth noting.