Actually, given the events of the last few years, it's entirely possible to stop paying the mortgage on your house by pleading ignorance to the documents you signed.
More to the point -- regardless of the specifics of the law, the persistent desire of this forum to correlate legality to moral correctness is somewhat disturbing. What does it even mean to form an agreement with "Google"? Even assuming the historical basis of contract law, what constitutes "consideration" in an agreement like this?
Personally... I don't see any ethical reason to perform negotiations with organizations that have become as large and as disconnected as Google. I speak to employee after employee and they all speak of Google's commitment to privacy, to openness, to not doing evil; but the actions of Google at every turn display otherwise. A man can make an agreement with another man or perhaps even with an organization that is capable of coherent action, but Google is neither. No "agreement" with Google is valid if only because Google is not a collective that one can actually negotiate with, never mind that it's proven time and time again willing to discard agreements and promises in the name of profit.
Finally, the statement is often made that if one chooses not to consider Google as an entity with which one can negotiate, one should simply not utilize their resources. Why? Because we can't negotiate with a mountain, should we fail to mine the minerals therein? Google is a mound of computational power and data with no remaining hold on human morality or ethics -- anything we can retrieve from there is salvage. Take it and use for the betterment of humanity, because they certainly will not be doing so.