If you deal with UNIX networks or the Internet, it's well worth adding to your library.
The Networking CD Bookshelf is a CD-ROM reference, aimed primarily at UNIX network administrators. The package consists of a CD-ROM containing the text from six O'Reilly titles; DNS and Bind, TCP/IP Network Administration, Building Internet Firewalls, Practical UNIX&Internet Security, sendmail Desktop Reference and sendmail, together with a hard-copy of one of the books; in this case it's DNS and Bind (3rd Edition).
The full text and diagrams from the latest version of each book is stored on the CD in HTML, together with a master index covering all of the books. Each book is then viewed and navigated using a standard Web browser. A Java application (and interpreter for most UNIX and Windows systems) is also included enabling all of the text to be quickly and easily searched.
If you intend to read any of the books cover-to-cover then you will probably still need to purchase the paper versions, but its intended function is as a concise reference. If you deal with UNIX networks or the Internet, it's well worth adding to your library.