The guy this morning also mentioned how the first things printed on the printing press were designed to look as much like manuscripts as possible, with people even drawing on them afterwards so they looked “right.” And how it wasn’t really until Luther (I don’t know if this is true; I doubt it, but I’m hoping NM will come by and shed some light) that books actually began to look like books.
His moral was then that we don’t yet know what electronic scholarship will look like because we’re still so busy just trying to replicate the book experience in an electronic medium.
Tiny Cat Pants 
Sheets far outsold books in North America in the 18th c, for a couple of reasons. Sheets were better for brief and timely and affordable communications. Likewise, until they stopped shipping all the cattle grown in SC to Barbados to feed sugar plantation slaves, there probably wasn’t sufficient leather in the British colonies to bind a lot of books. The early print industry in North America was geared towards circulating commercial news and reprinting political stuff, with the exception of reprinting Whitfield’s sermons and publishing almanacs. The dominance of the book as THE print medium was a 19th c development over here…don’t know what the story is in other places.
A lot of early printed books were designed to look like manuscripts. Printing was cheaper, you see, so the people who bought the books didn’t want it to look like they were buying a knockoff. And luxury manuscripts were illuminated, so you’d want illuminations in your printed books, too. But the manuscripts they were imitating were manuscript books (i.e. codices) — they looked just like what we think a book looks like.
What changed tastes from hand-illumination to woodcuts and etchings was technical innovation in the printing of pictures. There’s a coincidence in time with Luther (remember, one of the earliest best-selling prints was Durer’s portrait of Luther), but no causal connection.
Broadsheets were popular in Europe by the 17th century. They were cheaper (a single sheet or two) and topical (song lyrics, news, tales of marvels were popularized by broadsheet), but, especially in Protestant Europe, Bibles were big sellers as well. Of course, by the 18th century, literacy rates were much higher in North America than in Europe (around 1780, it’s estimated, about 50% of Frenchmen could sign their own names; even fewer women could read or write), so there would have been a much larger market for sheets here.