http://blogs.adobe.com/digitaleditions/
Although just a blog entry it seems that the iPad won't be using Adobe's drm but Apple's own flavour. So no good for library books or ebooks bought from other stores. Unless we do see some 3rd party apps with that capability.
"Although Apple has standardized on the EPUB format, because it employs its own DRM to protect eBooks consumers will lose out on much of the benefit of an interoperable format simply because they won't be able to transfer content across devices. "