Griffey showed many examples where Arduino-based hardware cost a third or even a tenth of retail goods. Assuredly some had added features and may have been more aesthetically pleasing, but even this customization is likely not far in the future, and as the software is open source, it can be modified to meet individual needs.
For libraries this serves two purposes.
First, it joins an arsenal consisting of 3D printers, knitting clubs, soldering torches, library farms, recording studios and other maker spaces. Some have asked whether these devices are just expensive toys with little in the way of utilitarian value. By incorporating devices that serve obvious real world concerns, it becomes easier (and more cost effective) to incorporate a maker space into a wide variety of libraries.
Second, as library budgets continue to be reduced in many communities, these devices offer an opportunity for cost-saving measures that unlike some open source software solutions will not see all of their savings lost through highly technical hours of labor.
Open source hardware is fairly new (Arduino and Raspberry Pi first came onto the scene in 2005 and 2006, respectively) and it is possible to overestimate their future impact. However, I believe that they have the possibility to inspire a new form of technical interaction for our culture, built not on consumption, but on participatory creation. Where better to start than your local library?