This can be a great tool if it works in a similar way to Bayesian filters by creating personalised corpi (plural of corpus) of words related to good and bad matches (rather than 'spam' and 'legit' corpi). So that by telling Google whether you like the search results or not, it can tailor future results to a context that is right for you. For example, if I do a search with the word 'java' in it, I may be interested in the computer language, coffee or the island. Different people search for different things using the same words.
It would also be very good at filtering what you consider spam results. And because it's personalised, it would make it very difficult for spammers to circumvent it, in the same way that email spammers find it very difficult to get past a good Bayesian filter like the one in Thunderbird.
And if you don't like it, you don't have to use it. Even if you use it, the day you want a context free search, just don't login to your account.