Word just came through the Feedburner blog that Google is now reporting on subscriber figures. This is a big step forward as marketers and webmasters have had to speculate on what we know to be a growing proportion of readers using Google Reader and Google Personalized Homepage to read blogs.
From the Google Reader blog:

Publishers [...]

The standard measures for web metrics - unique visitors and pageviews - don’t apply anymore. The technologies of the web, particularly Ajax, have made these metrics outdated. They no longer hold the same value to web owners or to advertisers.
From Seattle PI:

Ajax — the software trick used on the page, Yahoo Inc.’s e-mail service [...]