Ordering and relaxation in spin glasses are discussed in terms of the diffusion of the point representing the system in eigenstate space. On this approach, the spin-glass transition
Tg appears as a percolation threshold; stretched exponential relaxation behavior extends from
Tg to an upper characteristic temperature
Tc. Predictions are consistent with three-dimensional Ising simulations by Ogielski. Experimental data suggest that for real metallic spin glasses
Tc\ensuremath{\simeq}1.5
Tg. This approach may be relevant for other broad-spectrum relaxation phenomena.