Jeff Jarvis is at Ad:Tech and is liveblogging (or perhaps immediately-after-session-blogging) from some of the sessions. One tid-bit:

Doubleclick says 38 percent of Internet users account for 73 percent of pages viewed. That's what makes it hard to target across large audiences; you end up reaching the same people.

Good stuff, read it all.

Update: Jeff has posted about the blogging session.

35 million Americans, more than 20 percent of U.S. Intrernet users, read from 250 blog domains (that is, some large domains such as blogger.com and large individual sites; that mix does skew things a bit among big and small blogs)

More good stuff.