No one yet. Some of us have gotten close—jcgoble3 has gotten five in a row, but in a six-roll attempt, and I, among others, have rolled several Four-of-a-Kinds—I have five, personally.
And away we go! Going for fives... Nothing. Trying again. Holding 2s, rolling three die WOW! Luck ain't with me today! I'm gonna quit while I'm behind.
We're coming to the point where probability dictates that someone should roll a natural Yahtzee, very soon...
Well, there's been five of the same number in a row—with six dice being rolled—and there have been many, many Four-of-a-Kinds. I think I've had seven Four-of-a-Kinds myself, and there have been plenty made by others, as well.