We discuss the temperature-concentration phase diagram of doped La2CuO4. The addition of holes introduces a local ferromagnetic exchange coupling between Cu spins. The resulting frustration destroys the 3D Néel state characterizing pure La2CuO4, and generates a new 3D spin-glass phase. In the paramagnetic phase, strongly correlated Cu spins in the planes are canted by the holes, yielding an oscillating dipole-dipole attraction between holes. The possible relevance to superconductivity is discussed.