A possible explanation for the observed acceleration of the universe is a modification of gravity on cosmological scales. One promising idea along the lines has been proposed by Dvali, Gabadadze, and Porrati (DGP), in which we live on a brane embedded in a single infinitely-large extra dimension. Gravity propagates with different strengths in the bulk than on the brane, leading to effectively four-dimensional behavior on small scales. To date, this model is consistent with known experimental tests. I will discuss the evolution of cosmological perturbations in this model, and compare them with observations. We find a slight diminuition of the CMB anisotropies on very large scales, but it remains difficult to distinguish between DGP gravity and general relativity with current data.