I read that default RNG in phobos is Mersenne Twister. I think it would be a good idea to replace it with complementary-multiply-with-carry (cmwc). CMWC is faster (use simpler math), has a longer period (standard implementation has a 2^131104 period vs 2^19937 of current MT implementation in phobos) and passed diehard tests (mt passes them too)
And of course it's very easy to implement: http://en.wikipedia.org/wiki/Multiply-with-carry#Implementation
