Specific audience reach, timing by day parts will evolve as the Web moves from its still nascent marketing mode. In other words, trend data plus actual traffic reporting. Yes - we've seen it already among different sites. Third party monitoring is always a criteria for any area which desires to become a real ad medium. Site owned monitoring tools are valuable, but consistency in measures, definitions, etc are all very difficult to achieve as we have worked with a number of clients in this general area.
Every site counts things differently.
From our estimates, the ratios of users to sites remains fairly consistent. But clearly, there are major players with major audiences, major capital and major resources at their disposal. As time passes it gets more and more difficult for a site to come out of the blue and succeed - much more so than a few years ago. That s it for today, folks. Thanks to all who sent in questions, and thanks especially to Jim D'Arcangelo for taking time to give us a glimpse of how the Internet audience are growing.