This came up on Twitter, so I thought I'd expand a little bit but while I certainly enjoy my local public library branch I'm not certain that providing me with access to taxpayer subsidized comic books is a crucial public mission. A much more important public mission that I see happening at the branch is that low-income people are getting Internet access.
According to the Census Bureau there were 618,000 people in DC in 2011 of which 18.5 percent living below the poverty line. That adds up to about 115,000 poor people. The DC Public Library had a $35.8 million budget in 2011 or about $311 per poor person. That'd be enough to buy each poor person a low-end Verizon DSL connection with money to spare. But of course for most people Internet access is a household level expense not an individual one (i.e., my wife and I share a broadband connection) so it's unfortunate that the Census doesn't have data on poor households. The District-wide average is 2.12 people per household, but the demographics of low-income households may vary from that. All of which is to say that because of the presence of all these books and librarians, the public library is not a super-efficient way of delivering Internet access to low-income people.
I think the traditional justification for libraries as a general-purpose public service, by contrast, makes perfect sense.
It's in the nature of books that the vast majority of books any given person owns will not be in use at any given time. Under the circumstances, establishing vast municipal stockpiles of books for people to borrow is much more efficient than relying on a series of household stockpiles. But over time digital technology is eroding this rationale (the day has not yet come when every individual is equipped with a smartphone or tablet capable of reading e-books but it's quite foreseeable), and it makes more sense to shift away from stockpiling of books and toward things like the Oakland Public Library's tool lending program. I have a hammer, several scredrivers, a power drill, a hacksaw, and a bunch of other tools that I'm almost never using and households all over DC are in this very same position. The most successful libraries we be the ones who spend less time thinking "how do I extend my traditional reading-and-learning mission into the digital age" and more time thinking "what sort of club goods are being underprovided thanks to transaction costs, enforcement problems, and information issues."