On Tuesday, Google's stock price fell some more, apparently due to a comScore report that paid clicks were down. Henry Blodget of Silicon Alley Insider (who has been bearish on the overall economy and on Google for awhile) covers the news -- including a quote from a comScore skeptic. (We've also noted problems with comScore and all measuring services in the past.)

On Friday, comScore weighed in on their blog. Their data showed a clear decline in ad coverage during the first 4 months of 2007 which "clearly cannot be traced to a weak economy":

And, despite this decline, Google managed to grow its worldwide search revenue by 68% in 2007. (The company does not separately report U.S. search revenues.) The revenue growth was achieved through a 21% increase in revenue per paid click.

Read the whole thing for additional details on how the various factors may balance out.

Now let's back up a bit. On Wednesday, blogger SEO Black Hat posted: The Real Story: Why ComScore’s Google Clicks are Flat. Once you get beyond his fanciful setup, you get some hard data from a Jan. 4th post by Markus Frind (CEO of PlentyOfFish.com):

The CTR on text ads declined about 60% in the last 2 months with googles changes, Image ads on the other hand stayed the same.

(Obviously the 60% applies to Google ads on PlentyOfFish, not on Google search results or elsewhere.)

Black Hat concludes:

Adsense works in a Quasi-market place environment. The market will bid up the cost per click once the adjustment for accidental clicks is readjusted. Right now, marketers should be getting a better value per click as a higher percentage of the clicks are “real” or intentional. That will lead to higher bids per click and ultimately should be close to a break even for GOOGs bottom line.
...
[The] real story is that Online Advertising Spending will continue to grow at about 30% per year for at least the next 3 years and GOOG is poised to take a disproportionate amount of that growth even if nothing else they do is even marginally successful.