Today I came across two services launched by Google.
Image Labeler is a feature in game format where you can help Google to label images in Google index. So it will improve image search quality. This might be a older feature but I saw and played it first time today. Its really a good fun stuff.
Another feature, SearchWiki which is launched recently, allows user to customize search results. From now onwards, you will be able to see a "Promote" and "Remove" buttons after each search result. You can comment and see other searcher's comments on search results. You even can add any missing urls in the result too. The changes you made will only affect your own results. But I guess it will provide Google some feedback to improve its own ranking process.
I really liked the clever way of getting users all over the world themselves involved in this whole process so easily. Hats off to Google !!!