Andy Oram has posted an ONLamp article about OpenReader, a project directed at developing a page-based text reader for books, periodicals, and research papers. According to the features table, OpenReader will handle the major ebook standards such as OEBPS, PDF, DocBook, and (of course) XHTML/CSS.
I am looking forward to following the interesting bookmarking, referencing, and annotation techniques which Jan Noring intends to incorporate into OpenReader. An example is the booklet concept, allowing related notes and images to be presented in a separate pane from the main text.