Well of course DADGAD is not the exclusive preserve of celtic music players. there are some great blues licks in there.

Artie Traum does a great couple of instructional DVD's for the stateside view of DADGAD.

Also I'd recommend Martin Simpson's little DVD about open tunings. Martin makes the point that all open tunings can pretty much be tackled with a similar bag of techniques. Clever guy. But easier to see where he's coming from than say Martin Carthy.

What C tuning is that Bryn?

I've had a go at CGCGCE, and i love that one Martin Carthy uses for Famous Flower of Serving Men - DGCGCD. I haven't really got to grips with his other tuning, which makes the guitar sound like a really old instrument - a hurdy gurdy or something.. To be honest, I can't really think like he thinks about folk music - which is at the root of it.

I think that the way you think about folk music will in the end overwhelm any technique that you adopt. Somehow you will end up with what is inside your head - how ever much brain damage one brings to the party!