I'm experiencing exactly the opposite so it goes to show that the devil is in the details. There are seasonal factors, niche factors, traffic factors, etc. at play. Somewhere out there, there are others who are succeeding and improving their earnings as well. This just seems to be the place to report downturns generally. January and February have been traditionally slow months from my perspective but this year is a complete role reversal. I do think the Adsense program is weakening but it's still a viable program and there has to be more to the picture that what can be seen here in these threads.
We participate in only two programs. Adsense and Ebay EPN. With the change at Ebay EPN changing to the 24 hour cookie, we saw a 50% reduction in earnings. Now with Adsense, curious to know what other options that are "comparable" out there.
Keep in mind that the only reason for reduction with EPN was their cookie change. Both eBay and Adsense have experienced earnings have consistently grown over the past 36 months. No changes to the site have been made with the exception of improvements which brought increased earnings and traffic.
I've historically seen short term drops in revenue as a month, quarter, or year ends. I assume that this may be campaigns set to expire and then it takes a few days (or weeks) for the advertisers to set new ones up, or extend the existing campaign dates.
Also, in some niches there is a fairly strong drop immediately after the Christmas shopping rush. Did you have a comparable drop last January 2013 vs December 2012?