So far, university presses as a whole haven't been too aggressive in developing creative eBook plans for their catalogs and backlists. Judging from this, and the pricing models that many have adopted for current releases, there appears to be significant fears of cannibalization of hardcover sales. Out of print rarities, of which there are many, might be usefully revived through eBooks, but I have no idea of the cost and difficulties (or the rights issues) surrounding the taking of pre-digital era academic books and converting them into professionally presented eBooks.
However, UNC Press has launched an interesting program that offers parts of books. This could be a useful and profitable way to sell, for example, single chapters from an essay compilation. I am less certain in my feelings about their packaging large excerpts from narrative histories, unless they make very clear what they've done. For instance, they are now offering a 332 pp. excerpted eBook edition of the battle history part of Rable's Fredericksburg study. I don't own a copy to check, but I seem to recall that less than 100 pages from this tome were devoted to the traditionally rendered battle history section, so there are definitely significant amounts of other-themed material included. Hopefully, the press consults with the author(s) on these matters, because one can certainly alter the tone and thrust of a narrative work with this kind of editing.
They are also offering appropriate collections -- such as the Earl Hess eastern theater field fortification trilogy -- in a single eBook. You can see all this for yourself here.
Around the web, David Woodbury has commented positively on this development, as well.