As the number of users accessing web sites from their mobile devices rapidly increases, it becomes increasingly important for libraries to make their homepages "mobile-friendly." However, to our best knowledge, there has been little attempt to survey how ready existing libraries are towards this upcoming mobile era and to quantitatively analyze the findings via data exploration methods. In this paper, using the W3C's tool, mobileOK, we characterize the mobile-friendliness of comprehensive set of more than 400 libraries with respect to locations (e.g., world-wide vs. US vs. EU) and types (e.g., desktop vs. mobile). Based on our findings, we conclude that majority of current libraries (regardless of locations and types) be not mobile-friendly at all (with low mobile-friendliness scores of 0.16-0.21). Using mobilization tools, in addition, we demonstrate that the mobile-friendliness of library homepages can be improved significantly (i.e., 67%-82%). As such, much more efforts to make library homepages more mobile-friendly are greatly needed.