Not only is it CPU-only, we just enhanced the hashing about a week ago to be, by far, the fastest CPU-mineable algorithm in the world. Many CPUs get over 100 MH/s. There is a 1 BTC bounty out for anyone who can beat CPUs using a GPU, and we are talking to people working on a GPU miner. So far, the GPU miner in progress that we know of isn't yet close to CPU performance, but it isn't finished. Indications are that if they do get close to CPUs, or by some unexpected optimization leap, beat them, they will not be so fast as to prevent CPU mining. The effort is open, so the community will be able to see as well.