Google has been experimenting with letting users reorder and remove search results. This may seem strange if you think that Google cares a lot about algorithmically ranking search results. The new options allow you to promote some of the results at the top of the page, hide the results you think are not relevant and add new web pages that are missing from Google's results. These changes are saved in your Google account and only influence your results. For now, the users who see the experimental feature are randomly selected.
These new personalization options can be partly recreated using a custom search engine. You can build a custom search engine for the entire web, that should include all the sites from Google's index. Every time you find web pages or web sites that are not very useful, but have good rankings, you can edit the search engine and them to the exclusion list.
To promote search results, check this option in the custom search engine's settings: "Add my Subscribed Link to this Custom Search Engine". Then create subscribed links for some of the terms you search often. Alternatively, you could use Google Spreadsheets to define a list of subscribed links. The subscribed links are also included if you use Google's standard search engine, but they're displayed after the third search result.