Are abstracts confidential during the review process? In an answer to a question about the confidentiality of reviews, I basically said you cannot reveal information about the review until the paper is publicly available. This question about revealing information after publication is making me rethink my answer. The question I have is, is the information (e.g., title, authors and abstract) that you are given to decide if you want to review confidential?

It seems to me that the process of agreeing to do a review is NOT 


Please review our reviewer guidelines (including confidentiality policies),
If you accept these guidelines please look at this abstract and let
us know if you want to review.


Rather, it seems it is 


Please look at this abstract
If it interests you, please consider our review guidelines.


This suggests to me that the initial information (title, authors and abstract in a non double blind review) are not confidential.
I checked the peer review policy of Nature and Science, I guess that should is the best we can get. The policy can be found here, here (both Nature) and here (Science).
A bunch of relevant quotes from the Nature policies:

As a condition of agreeing to assess the manuscript, all reviewers undertake to keep submitted manuscripts and associated data confidential...
Nature journals keep confidential all details about a submitted manuscript and do not comment to any outside organization ...
Referees of manuscripts submitted to Nature journals undertake in advance to maintain confidentiality of manuscripts and any associated supplementary data.

And some from the Science review policy:

Reviewers are contacted before being sent a paper and are asked to return comments within 1 to 2 weeks for most papers.
The submitted manuscript is a privileged communication and must be treated as a confidential document.

I would read it conservatively. That is, consider an abstract to be a part of the manuscript, hence the same rules governing general manuscript should apply. Apart from that, both journals state that in advance to being sent the manuscript, the (I guess still potential) reviewers agree to keep the matter confident.
I think an answer may also lie in the exact process handling review. First, a potential reviewer is invited and sees a title and possibly paper's authors. Then he/she has to log-in into a review system, but I guess, somewhere in the process accepts general terms and conditions which established the contract. And only then the reviewer sees the manuscript. I am not sure if all journals do it this way, but those I reviewed for did so. Well, besides some special issues handled outside the journal submission/review system, where the case would be unclear.

I just checked the reviewer invitations I received from journals in my field and I found that the only disclosed thing in the invitation e-mails was the submission's title. I must accept/decline to review and only afterwards I saw the manuscript, or its abstract.