Real books are definitely better than ebooks.

Despite the deficiecies of ebooks, the CD bookshelf is nice. You get a paper version of Perl in a Nutshell, in addition to the ebooks. The search features of the ebooks are handy for looking up something short. IME, On-screen reading is fine for light browsing of a text. However, longer material is unpleasant to read on screen.

When the CDBS was my primary resource, if I wanted to read a longer selection, I would just print out the sections as I needed them (duplexed, 2 "pages" to a side to save paper) and throw them in a binder. After a while it became obvious which books I was printing lots of, so I bought "real" copies of those books.

I found the CDBS to be a cost effective way to get my hands on a variety of good perl books, before I had time to build my library. YMMV

Don't forget to check used book stores, you might be able to find some real bargains.

Good luck building your library.