Good point. I don't know of a drug case in Australia (to date) where internet history has been used against someone directly in a court case involving small amounts of drugs, but it has certainly lead to undoings.
At the Uni I attend, last year a guy was sprung making drugs because he used the department computer to download from the Bee place and Rhodium. Someone picked up a paper he left lying around and that led to checking history, checking workbenches, checking cupboards and finally to him checking out of the department into the waiting hands of Police.
As for book restrictions being an infringement of freedom of speech; well whatever it's called banning almost anything is still a stupid antiquated reasoning IMO. My point is 99.99% of people intent on using, selling or making drugs, will not be put off by the non-availability of books, where-as serious academic research or even student projects may be compromised. Not to mention the applicability to Harm Reduction Education. My Forensics Lecturer was interested in looking at PiHKAL. In fact after leaving it with him for the term he designed a forensics lab exercise from it %)