Chris Soghoian has posted a data-supported open letter to the NAI about opt-out cookies that is well worth reading.
Chris writes, in part:
In particular, I would like to draw your attention to the widely varying expiration dates for the behavioral advertising opt out cookies supplied by the various NAI member advertisers. The opt out cookies for some sites last as little as six months, while others last as long as sixty years. This variability is not communicated to consumers, and as a result, many are unlikely to know that they must revisit the NAI web site and re-opt out every six months in order to maintain total opt out coverage.
I urge you to update the NAI Self-Regulatory Code of Conduct to require that your members adhere to a reasonable minimum expiration age for opt out cookies (I suggest at least five years). I also ask that you add text to the NAI opt out page to inform consumers of the shortest opt out cookie expiration, and make it clear that they will need to re-visit the site at that time in order to renew the opt out cookies.
Read more on slight paranoia.
Thanks to a reader for sending me this link.