ken_b - 2:58 pm on Dec 18, 2009 (gmt 0)

I wonder if the drop in CTR might be more related to a wider roll out of interest based ads. If I recall right, ASA has said the IBA was being rolled out slowly, so maybe by now it's more common.

I don't know what the cause really is though, but wish I did. Unless Google speaks up, I guess all we can do is guess.