Reading that the trends are "based upon just a portion of our searches" makes me believe
that the trend is based on sampling, and thus relative to the number of Google searches
overall (and thus *not* relative to its own history). That would explain a lot. There has
been a vast increase in Google overall usage over the last couple of years.
Another reason might be that the more common a term gets, the more pointless it becomes to
use it verbatim in a search. Using it phrases is a different matter of course but I doubt
the reflects fragments of phrases.
Google Labs admit that the product is "in the early stages of development". They probably
have a long way to go before the "trend" becomes meaningful to look at. In my opinion, the
"News Reference Volume" diagram is far more interesting the "Search Volume". That diagram
should be the major one.
My conclusion. This is not useful at all. Not yet.
Regards,
Thomas Hallgren