I just read the following article on Clickz:
In a bid to protect its members from e-mail fraud and phishing, and to offer consistency to commercial e-mail senders, AOL today will begin implementing Goodmail's cryptographic CertifiedEmail program and phasing out its IP-based Enhanced Whitelist.
As part of its e-mail security practices, AOL blocks the display of images and hyperlinks on most high-volume messages, except if senders are on the AOL Enhanced whitelist and maintain very low complaint rates. Beginning today, AOL will also allow senders who have undergone accreditation through Goodmail to display images and hyperlinks by default. Goodmail charges accredited companies a fraction of a cent per message sent.
As Richard Gibson points out in his comment to this post, David Daniels, Research Director with Jupiter Research, also posted on this subject.