Attended a workshop conducted by Andy Irvine at the Woodford Festival 12 months ago. He inspired me to play the instrument, and also espoused the virtues of GDAD tuning. I must admit that I have stuck with GDAE, but this thread is a great chance for me to review that laziness.
Philippa, is your open D tuning F#DAD?
For others who are cash challenged like me, I converted an unwanted 6 string guitar using instructions on that marvellous Website known as Home Made Instruments. Sorry, but I don't have the URL. It is possibly included in the Mudcat links?