My favorite library in New York City isn't the main NYPL building at the corner of 42nd Street with Fifth Avenue. Instead, it is the much smaller but much more lovely location on the Lincoln Center Plaza, which houses the New York Public Library for the Performing Arts. This is where I browsed through Isolde 39 by Nicole Casanova, an out-of-print rather hagiographic biography of French soprano Germaine Lubin, on whom one of my characters (Yvonne) is very loosely based. This is also where I picked the old score of a Beethoven symphony in the stacks and admired the notes on paper that I had listened to so often.
This being said, I haven't used libraries much for my writing projects. Whenever I've found a book that seemed to offer a particularly valuable perspective, I've bought it - it didn't happen as often this time as for my previous novel, where I had to learn a lot about physics - and I've been fortunate to locate the other details that I needed to get right on the Internet. (You just need to know where to look and which sites to trust. The fact that I speak French has also come in handy, given that the novel is set in Paris and that I did have very good ideas of what I was looking for.)
I've also watched YouTube videos to decide whether I wanted this or that aria mentioned in my book. As an example when the Madeleine character returns to the Paris Opera at the Libération and sings with the bass-baritone, I needed an aria that could match the interactions between the characters. In addition I've checked the IMDb database and others for the filmography of actors I wanted to mention, for instance for the playbills in the metro, when I needed local color. Again, it helped that I knew what I was looking for. I didn't need to learn that Jean Gabin and Simone Signoret had been French monstres sacrés in the cinema industry, I just needed to check which ones of their movies had been made before 1949. I hope this - as opposed to inventing the names on the playbill - will increase the appeal of my book to the reader.
It should come as no surprise, then, that I have a tremendous amount of respect for authors of historical novels who wrote before the advent of the Internet. I can't even begin to fathom the hours they spent in libraries to get access to material - the hours they had to wait for a book to get shipped from another library so that they could consult it, the hours they wasted in front of the copy machine (when libraries started having copy machines) to make an accurate record of this or that background element.
I doubt I would've been able to write my book in the US if the Internet hadn't been there to help me bridge the distance between Bethlehem and Paris. As more and more material becomes accessible on the Internet, in no small part through Google Books, more and more writers will be able to consult high-quality material they might not even have known about before. They will then be able to write the books that match the story they have in their head, instead of having to content themselves with something less information-intensive, more within their reach. In that sense, the Internet - often viewed only as a source of distraction, by myself included - is truly a blessing.