Google SERPs Layout Changing?

I’ve noticed over the last few days that some Google results pages have no AdWords ads at the top of the page but they do have some as a footer. Its not apparent on every search but has certainly caused a noticeable drop in AdWords traffic for some clients. We’ve seen Google experiment with this layout before and presumably they have worked out how much it affects AdWords so I’m not at all sure why they are experimenting again now.

ppc ads at foot of SERPs