The bark is good for carving, put it on eBay. I paid my business insurance one year with cottonwood bark as a bet (long story, to prove a point about urban logging and not letting anything go to waste). Do a search for "spirit wood", 3 chunks 2" wide and 18" long usually go for $10.
The lumber shrinks alot when drying. It is hard to stain, best used "natural" (which is a boring, grainless white IMO). I make work benches out of it with thick (2") replaceable tops. The wood is soft enough it will not dent whatever you are working on, but strong enough to take some abuse. Once the top is shot, replace it.
I know a guy who paneled the inside of his workshop with 1/2" boards he had milled after he cut down a biggy that was where he was planning on building the shop. I have heard rumors of it being used as framing, but cannot vouch for that because I don't think it will hold a nail/screw in that application.
As far as "unstable" I don't know exactly what that means. It dries flat, and air dries well.
I think projects are only limited by your imagination. It is not a hard wood (even though it is classified as a "hardwood"), softer than pine but it has bending strength unusual to most woods. It will take a load without breaking lengthwise because of its flexibility and interlocking grain.
I am no expert on cottonwood, I really try to avoid it for myself I am surrounded by other woods that interest me more. I think there is another guy here who mills that may have more input.
One thing about it, it will not rot this winter until you figure out what you need, then have it milled to suit.
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