This past month I witnessed as traffic from Yahoo Products for a client increased 25 fold with no increase in conversions. After a short look through referral URLs I was able to find 1,000's of clicks from contextual pop-up ads delivered by Vibrant Media.
This was not an opt in, nor was there any notice I received that this would be happening.
Ads are linked to a single word on a page of content. Then an ad pops-up with just one product when the lin is hovered over, but if you click the text link before the pop-up you are taken directly to the advertiser page and a click is charged. Seems completely removed from the comparison shopping engine you expect when participating in Yahoo Products.
Anyone else seeing this? If not, be very wary of your traffic and look out for sudden spikes due to being "featured" in an ad. I have called Yahoo and they can remove you from Vibrant's ads and they seem willing to refund the click charges.