Google Searches Used in Murder Trial

It seems that the content of Google searches were used to help establish intent in a murder trial.
Will police in the future simply serve a subpoena to Google to find out what you've been thinking about? While this use of that information makes sense, at what point does your privacy give way to public concerns? Should police be able to search through your search history for "questionable" searches before you've been arrested for a crime, and what effect would this have on the health of society?