Wow, reading through this post really makes me appreciate how badly we need some flyable days....
Simon, as a paragliding pilot and instructor, and someone who sails regularly, I'm having a hard time seeing how paraglider dynamics are a combination of traditional flight and sailing, as you've proposed.
As was mentioned before, the vector addition from the combination of forces is quite different in a sailboat than in any aircraft (that I know). In sailing you have air moving above water, with part of the vessel in the air, and part in the water. It's the combination of these forces, in these dissimilar fluids, that allows us to sail upwind, with our most efficient point of sail at some angle off the wind. I don't see anything similar to this environment when we're flying.
I'm with the others on this one..If I want to head upwind, assuming the airmass is uniform (not in a localized compression zone, sinking air, etc), I simply point that way. Crabbing is great if I want to go someplace other than directly upwind. Landing directly into the wind is a good idea too
Having said all that, I think theory is pretty limiting without physical examples...how bout this, let's all go sailing one afternoon after flying, and then finish the day off with those beers??
Cheers,
Doug