The long awaited 28th edition of Nestle-Aland's Novum Testamentum Graece will likely appear some time later this year. It has been preliminary announced by various booksellers. Thus, CBD gives the publication date 26/12 2012, whereas Amazon has 31/12 2012.
The fullest description I have found so far is in a new catalogue from the German Bible Society (in my translation) where the publication date is September 2012:
After years of preparation the new edition of Novum Testamentum Graece ("Nestle-Aland") is now published. Thus, the world-wide standard edition of the Greek New Testament has become available in a fundamentally revised and improved edition.Publisher: Institut für Neutestamentliche Textforschung, Münster / Deutsche Bibelgesellschaft, Stuttgart
A main focus of this revision is on the textcritical apparatus, which has become better structured for increased clarity. For example, the reference to variants with sed or et and the differentiation between consistently cited witnesses of the first and second order, respectively, has now been abandoned. In addition, this edition for the first time includes the readings of the newly discovered papyri, registered as P117-127, which especially in Acts open up interesting perspectives.
A [another] main focus of the revision has been on the Catholic Letters, whereby the adaptation to the Editio Critica Major edition (ISBN 978-3-438-05605-4) has entailed over 30 changes [to the critical text; cf. an overview by W. Willker here]. The reference passages in the margin have been systematically verified and extended, especially with references to early Jewish literature.
NA28 will be available in the following variants, all in the format 13,3 x 18,7 cm:
Blue hardcover (1008 pp.), ISBN 978-3-438-05140-0: €28
Black leather imitation, ISBN 978-3-438-05155-4: €38
Blue leather imitation, ISBN 978-3-438-05156-1: €38
With Greek English dictionary (1239 pp.), ISBN: 978-3-438-05160-8: ca €36
With Greek-German dictionary (1219 pp.), ISBN: 978-3-438-05159-2: ca €36
Greek-English edition (1728 pp.) with New Revised Standard Version and Revised English Bible, ISBN: 978-3-438-05162-2: ca €45 EUR
I have no information about the planned CD-Rom which would link the text and apparatus of the digital Nestle-Aland with additional transcripts and apparatus published on the internet.