The Word of Mouth Marketing Association has recently made public a "Discussion Draft" of ethical guidelines around blogging. The entire draft and supporting documents can be found here.
And here's what the 10 point checklist looks like:
1. I will always be truthful and will never knowingly relay false information. I will never ask someone else to deceive bloggers for me.
2. I will fully disclose who I am and who I work for (my identity and affiliations) from the very first encounter when communicating with bloggers or commenting on blogs.
3. I will never take action contrary to the boundaries set by bloggers. I will respect all community guidelines regarding posting messages and comments.
4. I will never ask bloggers to lie for me.
5. I will use extreme care when communicating with minors or blogs intended to be read by minors.
6. I will not manipulate advertising or affiliate programs to impact blogger income.
7. I will not use automated systems for posting comments or distributing information.
8. I understand that compensating bloggers may give the appearance of a conflict of interest, and I will therefore fully disclose any and all compensation or incentives.
9. I understand that if I send bloggers products for review, they are not obligated to comment on them. Bloggers can return products at their own discretion.
10. If bloggers write about products I send them, I will proactively ask them to disclose the products’ source.
Well, there you have it. It's all about disclosure and transparency. Marketers, PR firms, Agencies (and bloggers) everywhere—do yourself a favor and read up on these. You'll be better off knowing they exist as opposed to claiming ignorance.