As an example of level of detail you need to know about Adobe products in order to read their e-books, see Fictionwise's
Adobe Reader eBook FAQ. Instructions that include software version numbers are not typically needed for other kinds of e-books. On the other hand, until I read this FAQ I did not know that Adobe Reader 7.0 reads Adobe e-books on the Mac (it does not do so under Linux, for example). There are relatively few e-book reader software options for the Mac, so that is a plus.
If you have both Adobe Reader 8.0 and Adobe Digital Editions installed on a PC, I think Adobe Reader (more or less) transparently passes you to Digital Editions when asked to open an e-book. However, Digital Editions is a very basic e-book reader - particularly compared to the Desktop versions of most other reader software.