You can read about it here.
You are allowed to opt out of this feature. If you do that, your ads will not show up on competitor listings though.
So what are your opinions?
Is leaving this feature on a net positive (due to exposure on competitors listings) or a net negative?
Or do you think it is just one more thing eBay is doing to confuse potential buyers?
If you haven't taken a look at the new listing format, you probably should. Instructions for seeing it are in the link above.