In November, the IEEE released a new copyright agreement, that is to be signed by the authors of all papers published by the organization since January 2011. The main novelty is that the authors are not allowed to publish final versions of their papers on-line. Fortunately, we still may post the versions accepted for print (with post-review corrections), which is still great, indeed. You can find the FAQ concerning the new policy here.
It seems the IEEE realizes that nowadays there is almost no need in their printed materials and the digital library as search engines manage to find papers posted by their authors. No doubt that they do not want to restrict dissemination of scientific results, but that is a question of their survival as a major publishing organization. The worst is they use the drug-dealer strategy: first they organize great conferences and journals (the majority of top venues in my field are run by IEEE), and allow authors to re-publish anything on-line ("the first hit for free"), then cut it off. Yes, one still may post an accepted version, but who knows what is their next step?
The IEEE motivate their decision by preserving the value of their database: "the IEEE is better able to track usage of articles for the benefit of authors and journals". One can object that there are big and growing open-access databases like Mendeley, where all the statistics is open and refined (the personal info of users is known). Also, not all institutions have an access to the library. For example, my university (the largest one in Russia) does not. And I cannot afford to pay $25 per paper.
What can we do about that? Sure, it is impossible to stop publish in IEEE venues, although the community can find the way around, as was demonstrated by the founders of JMLR, now the major journal in machine learning, which was created to cancel the overhead of the commercial publishing model. Matt Blaze encourages the researchers not to serve as reviewers for IEEE. As for me, I'm too young (as a researcher) to be a reviewer.
But it also has effect on me: I am now preparing a final version for the proceedings published by the IEEE, and I doubt if there is any use in improving my paper (even given a quality review), assuming that majority of researchers will use the accepted version and will never see the revised one.
UPD (Mart 14, 2011). I should have misunderstood the new policy at first, Blaze's post and IEEE terminology somehow misled me. The accepted paper means accepted for print by the IEEE, not the submitted for review. So, you still can use review results to correct the paper and post it on-line, then submit for publishing, where the formatting will probably be adjusted. So, any meaningful part could be reflected in the on-line version. I have corrected the post now, so it may seem weird.