I'd like to be more specific, but the article I read wasn't. Or rather it was an editor's comment, a short piece of information in an IT magazine. Most likely the comment was inspired by the WOT case.
Anyway, the point is to stay alert and double check any add-ons and other installs. There's too many fishy partners in the Internet, promising you the princess and half the kingdom. A published source code can be considered as a proof of reliability. Good reviews in several reputable sources being another.
Oh, and I use Adblock, too, and Disconnect. They do a marvelous work for disabling the misleading green "download" buttons on reputable help sites such as bleepingcomputer. As you hinted, the type of ads may not be monitored.