First of all, the distribution is NOT even. From what we can tell, the dark matter is concentrated, like ordinary matter, at the galactic cores. But it is more spread out than ordinary matter. It is the lack of evenness, by the way, that allows us to use gravitational lensing to map out where it is. But this is on the galactic scale of thousands of light years and up.
This leads to the answer to your other question. At the level of the solar system, the dark matter *is* spread out fairly evenly and has a density that is pretty low. As opposed to ordinary matter, which is concentrated in things like stars and planets, dark matter is spread out between the stars. Hence, at the level of the solar system, the effects of dark matter tend to cancel out: there is just as much in one direction as any other.
That said, the observations inside our solar system are one of the tight constraints that alternative explanations for dark matter tend to have problems with (like MOND, for example).