The problem with ebooks is that they mostly use the same format and layout as regular books. That will never be more efficient. The truly useful ebooks have additional features - bookmarks, searches, enlargeable images, etc. I use print books when I can. The few exceptions are the later volumes of RIC (I use Helvetica's spreadsheets) and Krause 1800-1900 and 1900-2000 (I use the official pdf's).