I've toyed with using these rules for books:
Using Books:
1. The quality of a book is rated as a skill bonus, e.g. +5 or +15. Note that quality is not dependent on length. A short scroll may present more useful information in a more useful format than a long and rambling journal.
2. Reading a book: within one month of reading a book, the character may call upon the book for a bonus to applicable skills until three successes have been achieved. This represents knowledge picked up during a quick read of the text. (If the skill roll fails, the book had no relevant information, so the opportunity is not expended.) The player should justify how the book's topic is applicable to the matter at hand. (Or the book may be defined as being about a given skill.) Reading a book takes 1 hour per 30 pages. (This is slower than readers of modern books; assume that your typical text is harder to read because it is likely hand-written, and non-fiction is slower to plow through than fiction.)
3. Studying a book: a character may make an extended study of the book, cross-referencing it against their other sources of knowledge, in order to develop a skill. A given book may be used to develop 1 rank per +5 bonus in a skill applicable to its subject matter. Studying a book takes 1 hour per 10 pages.
4. Referencing a book: if a character has a library of books applicable to their research, and can take time to consult them, these grant a bonus to lore rolls. This takes one hour per five books, and the bonus is +1 for every +5 bonus of every book used. This bonus is never used up.
I think this makes them worthwhile but not too potent, unless you want to haul around a huge library which has its own issues. It also creates a new and interesting class of treasure.
There are some example books here: http://www.guildcompanion.com/scrolls/2012/dec/tomesofpowerlapidaries.html
There's a nice random book generator included with Inspiration Pad Pro, that comes up with titles, authors, page length, appearance, and quality, e.g.
Obirn, A Concise Biography, by Telendiel
180 Pages. a well bound book, with an illustrated wooden cover. The title of the book is plainly marked on the cover. The paper pages of the book itself are bound by a metal latch. The penmanship is poor, but pen strokes clear. The book covers it's subject well, but could be better
I customized it for my setting and also added language etc. I recently had the players gain the favor of a noble with a personal library, I gave them a list of 24 books (mostly random but I picked the ones that were most appropriate for his interests) and told them they had time to read one before they move on. A nice short term reward.