Language revitalization efforts are near and dear to my heart. The situation of the Celtic languages and Ireland's place specifically is distinct from similar efforts in the Americas and the anomalous case of Hebrew. (Where can I find a book-length treatment of Hebrew's revival into a daily language? I need to read that.) This book covers the whole story, from the middle ages until its publication (ten years ago), and its central observation—that economic, material conditions were and are the reason for the dying of Irish—is one I'd never heard before.
I'd give a limb for a comparative study of language revitalization efforts. Imagine something that treated the Celtic languages, both North American languages and Polynesian languages (i.e. tongues spoken in former British colonies), revitalization efforts in Latin America, especially South America like the state-sponsored programs in Venezuela or the status of large languages like Quechua and Guarani, and Modern Hebrew. That would be a perfect book.
In the meantime, though, this book has given me what feels like a key piece of the puzzle.