When in The Nether in the 1.5 pre-release, I had the misfortune to encounter lava which a.) flowed at the speed of water b.) could flow the same range as water, but still c.) remained flowing for a long duration after the source was removed d.) killed me at lava's regular speed. The effect can be produced with any lava in The Nether, weather it is naturally-occurring or from a bucket. The effect is consistent in both survival and creative modes. Lava behaves normally in Overworld