Pooks - the library is one of my favorite places to ride so please try it. Get a good lock or two and/or take the front wheel inside with you. If there's foot traffic going by the bike rack (other library patrons) that should help deter theft, too.

I have panniers and a back rack on my "errand" bike. I don't usually use the pannier for books -- just a bungie cord or two and strap my books to my rack.