it's been a while, I thought I'd resurrect this thread, as we've started our 2011 yacon harvest.
last year we had six plants (after giving a few away), but most of the tubers got frozen (storing in a spot we didn't think would freeze), so I was too irritated about the whole thing to post about it. this year we had 20 plants, and they've done quite well with a layered leafmulch-and-comfrey mulch around them. dug six plants a few days ago and got most of two 5-gallon buckets full of tubers, and another half-bucket of rhizome for next year. will keep digging the rest as I get a chance - they store quite well in the ground where they grew unless the ground freezes deep enough to get them...pics will follow when I can, looks like we'll have several hundred pounds when all is said and dug.
I've found that the flavor is best if after washing the tubers off, you let them dry, and they sit at room temperature (even where the sun will hit them a bit) for a few days (or weeks - they last pretty well, though they soften a little after a while). the skin takes on a nice earthy-purple color after a bit, and the flavor gets both sweeter and more complex.
this past summer, I did try a tea of the leaves, which HGscott mentioned you could do earlier in this thread...it's startlingly, unpleasantly, bitter...so I imagine it's as good for you as they say. I think I'll stick to the tubers.
I will have some rhizome available for sale, for those with a long enough season, and relatively near to me (I'm in western NC, and don't really want to ship them far - I'd rather be more sure the quality stays super-high), either this fall or in the spring. message me if interested.
will update with pics as I get them together.