Last year Google updated their AdWords trademark policy in the US. The aim was to allow some non-trademark owners to use trademarks as keywords for their PPC advertising without having to get permission from the trademark owner.
In summary if you sell a branded product, parts or more controversially a compatible product (e.g. a Canon compatible printer cartridge) then you can now use the trademark as a keyword and include the trademark in the advert text, all without getting permission from the trademark owner (e.g. Canon). (More here from us and the official announcement)
As with all of the AdWords trademark policy bear in mind that the policy is designed to protect Google, not you the advertiser! i.e. the trademark owner may be able to sue you successfully, even if they can’t sue Google. Case law is still developing on this and especially in light of the recent Portakabin case, I am seeing quite a few different legal interpretations around so care is still needed.
However we have a number of clients who will benefit from this change and we see little reason, not to take advantage of this.