There are few easy-to-attain signals that will help you to differentiate search results in a way that approximates the opinion of an intelligent human.
I believe we have reached the point in which Google's search results are only useful for one reason: speed of information retrieval. If you wish to get high quality information you visit sources that you trust. These are either (a) content providers that have provided high quality information to you previously, or in the cases in which you've not had to search for some information before (b) socially curated information from user communities in which you trust and are a part of.
Here's an example: http://www.google.co.uk/search?q=mp3+player+reviews
Most of the content rated highly by Google has either nothing to do with reviews or is hideously out-of-date, note the 2007 'reviews' in the second result down. It's junk all the way down. For a lot of people the Google search bar has been denigrated to a fancy URL bar; it takes them to places only when they know where they're going: you avoid browsing for fun.
So what can be done... An extension that allows you to join an invite-only group of Hacker News users who will remove any rubbish search results from Google? Using the +1 as a signal to try and make the search results better? I can only see the former idea as being difficult to game. The latter would be unused apart from for very popular searches to the extent that a determined spammer with a botnet wishing to cheat would probably be able to affect many search results.
Better minds might know better ways.