PR Opinions unearths the unseemly practice of paid advocates - the kind that you don't hear about as having been paid:

Appearing on a local TV show in Austin Texas to review toys for kids, Oppenheim promoted a number of different products including a  personalized photo album from Eastman Kodak.

The only problem was that Mr. Oppenheim was paid by Kodak.

On a subsequent appearance on NBC's Today show, he once again promoted Kodak's product - though Kodak says it didn't pay for that particular mention.  That was obviously Oppenheim's favor to Kodak. And they weren't alone.  Of the fifteen products he plugged on NBC, nine were former clients and eight had paid for plugs on local television.

The Oppenheim episode has opened up a big can of worms.  It appears that there's a booming industry for TV talking heads promoting products for cash with no disclosure before, during or after their segment.

Infomercials are better than that - at least they don't hide the pitch. It's only a matter of time before this happens in the blogosphere (more likely, before it gets reported as happening). There have been bloggers paid for political mentions (from both sides of the spectrum) - I'd guess that there are bloggers getting paid for product mentions as well. Easy enough to do, actually - a blogger with a passion for something (photography, say) gets offered money to slip in mentions of a particular brand/model. I don't see any obvious way for general readers to find out, either.