All excellent points. Thanks for posting this. I agree that 2 months should never be a cause for alarm for something like this. It's only that for so long they

All excellent points. Thanks for posting this. I agree that 2 months should never be a cause for alarm for something like this. It's only that for so long they had been able to keep building significant continuous improvements in clickthrough rate that makes it a potential warning sign. At some point, clickthrough rate could actually end up plateauing on an ongoing basis as they run out of ways to keep improving the rate. Then their ad business would be solely dependent on impression growth (which I assume would still be fine) for clickthrough growth. Of course, as you point out, referral quality is also an important factor, so even if they get the same number of clicks, that might be great for advertisers if it's better traffic. Is this the end of growth in clickthrough rate? Unlikely. But it's always good to keep an eye on these things in case it turns out to develop into a trend.