There are sometimes when you may come across websites whose content may not really be that good but who show up in the Google searches you undertake. Now, there is no easy way to get rid of those results unless you filter them out using some sort of user scripts.
However, starting today, Google is making it easier for users to start blocking websites from their search results with the help of a Google Chrome extension called Personal Blocklist. Using this Google Chrome extension users can easily block websites from appearing in search results. Once a website has been blocked, they will not appear in Google searches you make in future.
When you block or unblock a website, the extension will send information about the URL to Google. There is no way you can change this behavior.
You can also unblock the websites by clicking on the extension icon and unblocking the website. Overall this is a good feature if you want to remove some sites from search results.
Problems With Extension
According to Matt Cutts, this feature may be used by Google as a potential ranking signal in future results:
If installed, the extension also sends blocked site information to Google, and we will study the resulting feedback and explore using it as a potential ranking signal for our search results.
This would definitely not be a really great idea, because people will then just start paying others to install the extension and start blocking their competitors websites. If Google starts using such data for ranking search results, it would be a disaster at best. I would prefer using the extension as a personal choice rather than overall Google rankings.
If you are interested in trying out the extension you can download it from here.