Google drops SearchMash (Google's experimental non-branded search interface) in favor of SearchWiki, a new functionality that allows those with Google account to customize their search results. With SearchWiki you can move specific results up or down in rankings so that they will appear in the preferred order when you do the same search in the future. You can also post comments on the results of your searches. Not only that, you can also see what other people have said on them also. The comments and notes that you add will only affect your own search.
According to a post in the official Google blog : "This new feature is an example of how search is becoming increasingly dynamic, giving people tools that make search even more useful to them in their daily lives. We have been testing bits and pieces of SearchWiki for some time through live experiments, and we incorporated much of our learnings into this release. We are constantly striving to improve our users' search experience, and this is yet another step along the way."