A post in WebmasterWorld says Yahoo! has deleted all his 2005 PPC data. The report says:
"I just got off the phone with an support rep from Yahoo. I was trying to pull some data from the old Overture system from 2005 and none of the reports were pulling up. The rep said that this data was deleted from their servers because they needed to make space for some other things."
This is the first case reported so far.