I think physical collections of printed-type materials will slowly go away. It is truly sad, but probably inevitable in the long-term. The publishers can’t stop the digital revolution forever, and they will be forced to provide the materials people want, and if they refuse, more and more authors will just do it themselves, because it really is easy today. Yet, when this happens I fear it is going to be devastating for physical libraries. Once the vast majority of materials that people use (not everything) is online, fewer and fewer people will need to come to physical libraries, except as a place to meet people, do their email, take a class or two, and managers are going to have to reconsider the purpose of maintaining the very expensive physical collection.
I personally think it is a bit too soon to get rid of 75% of a collection, but I could see that if there is a digital copy on Google or the Internet archive or one of the umpteen-zillion digital sites on the web, you could very probably get rid of your own copy. So, I could see that physical libraries will become archives and maintained and protected for a time of emergency, if something happened and all of Google Books sold to the Chinese or all of these other sites got wiped out somehow. All of this could happen very, very quickly once they come out with a good, cheap ebook reader and when the Google Books agreement is ratified , especially if it takes place duing the economic crisis and tough decisions will have to be made.
Still, as I keep pointing out, it doesn’t necessarily mean that librarians will fade away with libraries. Those who see their jobs as primarily maintaining a physical collection, they are true dinosaurs, but if you think of librarians as those who select and organize information and help people find it, I think there will be lots of opportunities. I remember I worked with a graduate student in architecture at Cornell, and he asked me what I thought the library of the future would look like.
I said that I thought it would be like the ancient Roman baths, where people would go to work out, get a massage, bathe, meet people, eat a little bit, shop a little bit, but there was always a library attached. If you look at Wikipedia on the Baths of Titus, they have a picture of the library: http://en.wikipedia.org/wiki/Baths_of_Trajan
I could see something similar in the future: the librarian would have offices with computers hooked up to the internet in some mall or metroplex or wherever lots of people go, and people could go to them for quality help they can rely upon, and they can be assured that these are not people just trying to pick their pocket. Maybe we could do some massaging on the side!