From Nov 2012 to January 2013, Google has till now released 4 Panda updates. The newest one is the one dated 22nd January 2013. Google does not want poor quality sites to rank in their search results. And by releasing Panda updates, they are just weeding out those sites that are poor according to their algorithm. Suppose a person is searching for something on Google and comes across a website that seems good. He makes a purchase and then he realizes that then realizes that his credit card is compromised. He can blame Google for ranking such a website on search results. Its just an example I gave you to understand what Google is aiming for by removing poor quality sites from their search results. I have got a checklist for you to understand what is high-quality according to Google.
I find that's hard to believe, credit card fraud...Please. I think Google just wants to promote AdSense.