I was asked, for example, whether this meant that agencies would have to start getting permission from clients to use the client's trademarks.
Not according to my understanding of it.
I feel qualified to answer this - since I was an editor at Yahoo, and was on the special team that was dedicated to reviewing trademark terms.
As it stands, on Yahoo you can advertise under any trademarked name as long as you have content on your site supporting it – such as a comparison of your product to your competitor’s. There is nothing in the change which indicates they will not allow advertising under the trademark name associated with the website doing the advertising.
This is designed to be sure that Geico can’t advertise under the keyword “progressive” – even if they have a page of facts comparing themselves to Progressive. This is designed to protect the interests of big name corporations who don't like PPC because competitors can use it to show up in search listings when a potential customer is looking for them.
Geico, whether directly or through an agency, will still be able to advertise under “geico.”
The place that trademark terms get sticky is on Google – where you can buy the term, but not put it in the ad unless you have written permission from each trademark holder – and while that is meant to prevent this kind of competitor advertising, often it ends up with situations where someone selling a product can’t use the name of that product in the ad. For example: MLB (major league baseball) is copyrighted. AcmeTicketReseller.com sells MLB tickets, but can’t say “MLB” in the copy. Or AcmeShoes.com - they are unable to use “kenneth cole” in the copy, even though they are selling kenneth cole shoes. If a shoe site sells 200 brands, getting written permission for each is somewhat prohibitive. These hardly seem like the kind of uses of trademark terms which threaten their integrity - since they make the trademark holder money, but that's how it's handled.
On the other hand, on Google, Geico *can* advertise under the term “progressive” – as long as they do not say “progressive” anywhere in the ad copy or imply in any way that they are Progressive. Now, this seems to me to be exactly the kind of thing that the big corporations want to prevent - their direct competitor showing up when a user is searching on their brand name.
Yahoo does not restrict trademark terms in this way – and it sounds like the limitation will ONLY effect competitors, not resellers. This has actually been a change they’ve talked about for over a year, as it was under discussion while I was still working there. The lawyers were evaluating it while I was there, trying to balance the choice between free speech and attracting large-name companies’ business. I personally would have preferred to see them lean in the other direction - as some legitimate consumer comparisons will end up getting shut out by this.
(addendum - per Yahoo, sites that offer a comparison can still advertise under a trademark term as long as they don't sell a product that competes with this... this will mean that some sites will get sneaky and try to hide their relationship to the product sales - but should protect legitimate consumer comparisons - BUT it means they will rely on editorial review heavily for these decisions, and editors, being human and having quotas to meet, do make mistakes.)