Books are considered a luxury on the trail, because they are heavy yet inedible. During my AT hike, I always carried books, sometimes two or three at a time. I mostly read paperbacks which were either mailed to me, or found in AT shelters or in town. I still have the torn-up copy of Edith Hamilton's Mythology I found somewhere in Tennessee. It was only fitting that on my last night on the trail in Georgia, I reread her telling of the Odyssey.
For the PCT, I plan to carry books, too. The challenge of long-distance hiking has two components: physical and mental. On the AT, they say that the first half of the hike is physical, and the second half is mental. If you can physically bear the first half of the trip, you can probably bear the second half. The bigger question is whether or not you want to finish the trail.
It's so easy to quit--it would take a few days to hike to a road, hitch out, and get on a plane or a bus. For me, I need intellectual stimulation to stay on the trail. I plan to always carry a book, and would welcome reading materials from my friends.
As for guidebooks, there seem to be a few common books to carry. Some people carry the Pocket PCT: An Elevation Guide to the Pacific Crest Trail. I haven't heard much about this one, and many of the maps are available online from halfmile's website. I like elevation profiles, but they are intimidating, especially in the Sierras.
My plan is to carry the official data book from the PCTA: Pacific Crest Trail Data Book. This is a minimalist, pared down book, mileage markers and water locations. It reminds me of the Wingfoot book I carried on the AT. The PCTA also has more extensive guide books, with full maps and written descriptions of the trails. There are three books total, one for Southern California, Northern California and Oregon and Washington. I highly recommend these books, which are have b&w photos and are lyrically written. Water access is also described in great detail, which I will need, especially in the desert.
The books are great but heavy. I've cut up the Southern California book and have sent the sections on in the first set of bounce boxes. I'll ask my family to send the rest of them along the way.