You would think that only newbies to Bitcoin google it so Google trends would only indicate new people interested in Bitcoin. However, with the news aspect of Google search many old Bitcoin users will also search for the term bitcoin again and again. As a result, the trend will be ever-increasing, don't you think?
I suppose that the number of google searches for bitcoin is probably a pretty good proxy measure for how many people know about bitcoin, not just the newbs. Like you said, old-timers will search for bitcoin on google just to make a popular site pop up now and again. Also, now that google has added bitcoin exchange rates to its currency conversion widget, that's another reason to google for bitcoin even if you're an old-timer. However, I suppose that at some point in the future, the number of people who know about bitcoins will stabilize and at that point the number of google hits probably will stop increasing.
