I'm busy right now with some poplar as well as having worked with it to a limited degree over the past 5 years or so. Actually, in times past, it was regularly and widely used in places like France, Belgium and Holland at least.
Anecdotally speaking, in France this timber was preferred over oak for use in horse stalls because it did not react to the ammonia given off by horse urine. Many a hay loft floor of the barns around here were poplar because of its wear resistance due to its long fibers which also makes it not such a pleasure to work with hand tools but it is true that working it dry helps.
My hay loft, which is now where I dry wood, has new poplar floor planks, 35-mm thick and some up to 40 cm wide at one end. It's stable given that it is dried with a bit of care. I use it whenever I can get a hold of nice straight looking trunks, and it's free.

Don W.