Weiser's landmark Scientific American article inspired many researchers to explore an exciting socio-technical vision of a third generation of computing. At the 21st anniversary of that published vision, I want to assess ubicomp's maturity and explore the identity challenge it faces. Today, ubicomp as a niche research topic no longer makes sense; we must celebrate its "disappearance" as a well-scoped research agenda because it has become a profound agenda across most of computing, and beyond. This should not be surprising; the 2^nd generation of computing, the personal computer revolution, experienced the same profound disappearance. In celebration of this imminent disappearance, I will highlight the unique contributions of the ubicomp community, express some remaining intellectual challenges, and speculate on how to formulate new visions of computing that might succeed this third generation.