There are three kinds of lies -- lies, damn lies, and statistics.

Daily pageviews here is probably the least useful metric to evaluate our site, given that Posterous doesn't chase pageviews and send daily subscription emails (full text bodies) to users directly. Users can also reply to comments via email without ever going back to the site. The monthly numbers are much more in line and reflect the way our users use the site.

Having a competitor be 4 million uniques ahead of you when you're 2 years into a consumer internet race? I dunno. Wordpress.com, by comparison, has about 160m uniques per month (per quantcast). Tumblr and Posterous are still in "small potatoes" country-- it's anybody's game.

4M vs 400K is a pretty wide margin. You also tried to compare growth rates which didn't exist. Finally you're also are showing a graph with Tumblr's growth climbing and postereous's growth pretty flat. If anything you just reinforced the point that Tumblr is leaving postereous in the dust.