Google addressed the recent concerns about smart pricing in their Adsense Blog. They didn’t, however, even address the big issue about whether or not smart pricing is calculated based on accounts, sites, or something else. Which would seem to indicate that it is calculated on an account level.

They do say that the clickthrough rate isn’t involved. They also say that more than the conversion rate is involved in determining ad prices.

In the Threadwatch discussion about smart pricing graywolf brought up the point that
“One poorly converting site can result in smart pricing impacting an entire account, even sites completely unrelated to the poorly converting one”. Google didn’t address this issue either.