A friend of mine works at a library, its.. ew what they have to deal with.
Sure you can put up filters, but the sheer number of sites makes it really difficult, and besides, you'd have to get someone to go to these sites to find them to block.
And Libraries, a lot of the information you had before is now online, though there are still many many MANY books not scanned (something Google was hoping to help). The librarians are themselves a resource on how to find information, not everyone's Google-Fu is great.
Most of the libraries I know of hold events, book readings, school and child education events too. I think they are still very useful if for a public resource and access to the internet for many people who can't afford a computer in a world where more and more is done over the internet.