signor_john - 2:12 am on Dec 10, 2008 (gmt 0)

My CTR and eCPM have been down, too. It's possible that Google has tweaked its definition of a "valid click," but I'd guess that the economy is the main culprit. I've seen a fairly significant drop in affiliate bookings since the global economic panic hit in September. (Display ads are going strong, but they don't depend on clickthroughs to generate revenue.)

On the brighter side, my average earnings per click are very high--the highest they've been in years--which suggests that AdSense should return to being a more productive cash cow when the economy improves and readers are more willing to spend money.