Opaqueness was always going to be a problem in the blogosphere.  Seems the UK is moving to make it a crime:

The rules make it an offense to blog, use brand ambassadors or seed viral ads while “falsely representing oneself as a consumer.” They also apply to bloggers who fail to disclose they have accepted money to write about a product.

“If advertisers and their agencies ignore the ethics of responsible advertising, the damage to the advertising and marketing industry generally will be considerable,” said Marina Palomba, legal director at the Institute of Practitioners in Advertising, the U.K.’s agency association.

Thanks to Steve for the pointer…