The Google AdWords has announced in their blog that a few changes are being implemented that will result higher minimum bids and better user experience. the changes will affect a small number of advertisers. In fact, only those advertisers who offer a poor user experience to those who click the ads.
This is to ensure better ad impact and stop click arbitrage. Many offer landing pages with nothing or little else other than Google or Yahoo! ads. Click arbitrage involves directing inexpensive pay per click traffic to their landing page and make them click on a high paying ad to exit. That is why such pages don't have any quality content on the page other than the ads or just enough content to influence the AdSense ads.
Take a look at the landing page and site quality guidelines from the AdWords Help Center. This is a set of useful guidelines which will help to define what users look for in a high quality site.