Google sent an email to many publishers yesterday, including myself, explaining a reporting issue with Google mixing up some of the earnings for link units with regular ad units. The email's subject line read, "Update to AdSense link unit reporting" and the email read:
As a publisher using link units on your pages, we're writing to let you know about a recently resolved reporting issue that affected your account.
We discovered an issue with the way earnings from link units were being shown in publisher accounts, which resulted in some of your ad unit earnings being incorrectly attributed to link units instead. However, this was only a reporting display issue and so your overall earnings and payments were not affected. We've resolved the issue, and as a result, you may now notice slight differences when you look at reports for previous months. Specifically, when you generate separate reports for link units and ad units, you may see that earnings from link units on a particular day have decreased, but that the ad unit earnings for the same day have increased by the same amount.
Again, please be assured that your aggregate earnings and payments were unaffected, so you've been credited for all valid clicks and impressions. In addition, this issue has not affected your ad performance in any way.
Your reports will now accurately reflect your earnings from link units and ad units -- we apologize for the inconvenience and any confusion caused.
So no damage was done on the earnings side. Some publishers who may have looked closely at their reports to make tweaks to their pages may be suffering a bit, but overall, this doesn't seem like a major deal.
AdSenseAdvisor in a WebmasterWorld thread added a bit to it:
Just to clarify, there was a link units reporting discrepancy that we recently cleared up. Aggregate earnings were not affected AT ALL. It's just that if you go back and pull reports on your historical performance, you may notice that a lower percentage of your earnings are now attributed to link units (and a larger percentage are attributed to regular ad units).
An email went out to all those who were affected, so I'm guessing a lot of you got it.
Your aggregate earnings have been correct all along, we were just a bit off in attributing them to link units vs. regular ad units. Now we've cleared it up and any reports you run now will correctly reflect exactly where your earnings came from.