I use DADGAD quite a bit, as well as a number of other tunings (including "Vestapol," otherwise known as Open D). The "augmented third" is more commonly known as a fourth, by the way. I find that DADGAD has a fundamentally different character than Open D, and in many ways is more versatile because it's tonality is not inherently "major". It is very well suited to a lot of Celtic music (imprecise term, I know -- please don't berate me for using it!). I believe it was invented by Davey Graham years ago. I find that it most often leads me to play in D (major, minor, or modal), which is something of a limitation -- but with some time and effort, one can find other keys to play in as well. It's definitely worth exploring.