Originally Posted by
beckoa
You bring up an interesting point here... that one can borrow a book from a library and take it on the trip too

I've done this more then once
It all depends if its in stock, how long your trip is, and if you can renew it if you need to...
Our local library has a two week rental with two renewals, and renewals can be done online. Just before I leave, I do a renewal so I have a fresh two week window. (The only time this doesn't work is when someone else has requested the book, in which case I have to get it back to the library before I leave.)
This is off-topic, but I also sometimes use the library's vertical files. They have pamphlets, maps, etc. sorted by destination and they put my selections in an envelope so I can borrow them.
Eventually, my favorite guidebooks will probably be whichever guidebooks are available for my ipod touch with maps intact.