Julian Sanchez takes issue with this chart, which purports to show Tumblr eclipsing "blogs" by reference to the number of Google searches for each:
[T]he ubiquity and integration of blogs means that "blog" is a much less useful search term for narrowing down your results … Tumblr, by contrast, is still ultimately one domain, and distinctive enough that if you saw something on a Tumblr, you’re apt to remember that it was a Tumblr, both from contextual clues about the site itself, and because there are still some very characteristic types of content that we associate with Tumblrs. So including "Tumblr" in your search terms is actually a really good way to quickly narrow your results …
His takeaway:
[T]here’s a general point here about how to interpret trends in online activity—whether it’s Google, Twitter references, Facebook likes, or whatever. The frequency trend over time can’t actually be interpreted straightforwardly without thinking a little bit about both broader changes in the media ecosystem you’re examining and how changing user behavior fits into the specific purposes of the technology you’re tracking. With search, the question isn’t just "are people interested in term X?" but also "is term X a useful filter for generating relevant results given the current universe of content being indexed?"
The Dish 