Google is giving users the ability to block sites that annoy them from ever showing up again in their search results, via a new link next to search results. This should help you block those spamming sites from your search results. The new links will be visible to English users of Google.com sometime starting this week if those users are using Internet Explorer 8 or 9, Chrome 9 or later, or Firefox 3.5 or later. Users of other web browsers will not see the new option. Non-English users will receive the new changes within a few weeks.
Google apparently is listening to the complaints of users that web results are being polluted by low-value content farms. The new system might even eventually change search results for everyone, according to a company blog post at http://googleblog.blogspot.com/2011/03/hide-sites-to-find-more-of-what-you.html
You can also later change your mind and unblock any sites you previously blocked.
The Google blog states, "We’re adding this feature because we believe giving you control over the results you find will provide an even more personalized and enjoyable experience on Google. In addition, while we’re not currently using the domains people block as a signal in ranking, we’ll look at the data and see whether it would be useful as we continue to evaluate and improve our search results in the future."
If you do not yet see the "Block all www.xyz.com results" in your searches, wait a day or two. The new changes are being rolled into Google's new servers in the next two days and will show in your searches soon, assuming you are using Internet Explorer 8 or 9, Chrome 9 or later, or Firefox 3.5 or later.
Full instructions are available at http://googleblog.blogspot.com/2011/03/hide-sites-to-find-more-of-what-you.html