I have the Resist Down in my winter quilts from Underground Quilts.
I don't notice any frost build-up on the quilts. However, I have seen frost on my hammock, on the sides (from my breath) and bottom (after I got out of the hammock). If I use the over cover, there is almost always frost on the cover.
I haven't noticed any loss in loft. It would be interesting to weigh them and measure the loft on them them before and after, but I haven't bothered to try it yet.