I've not heard that information on Poplar or I'd have been learning on it. Thanks for sharing that.
I've heard the general rule of thumb is that if it flowers (what tree doesn't- they've got to reproduce right?) bears fruit or nuts, that it's usually good to turn. Of course the guy who told me that doesn't like to turn Oak or Walnut... and has too much Pecan for his liking..
For myself I have three trees that will come down this winter. One is a wild Cherry that is diseased and is almost dead anyway. The other two are mutant ornamentals (hybrids). (I wouldn't neglect these kinds of freebies that come down in a neighbors or friends yard.)
One is a Bradford Pear that someone planted right next to a light pole and power line. So it's lopped off on one side, and looks ugly. I hear it turns nice though...
The other one is an ornamental Plum that has been on my hit list for several years just because it's generally unhealthy anyway. It has lovely blossoms for about two days a year, nice contrasty purple leaves for a couple of months and looks bad the rest of the year. Since it's twin did such a nice job spalting just before I took up turning.... And turns soooo nicely, I'm going to harvest and prepare this one on purpose just for turning.
I'm finding that turning small spindles is excellent practice, and I have lots of drops since I work in a cabinet shop... So I've turned several species of letter openers just for fun. Cherry and Maple turn really nice, Walnut I'm in love with, Alder is OK. I'm working on Mahogany one right now.
And I've found really dry White Oak to be the hardest thing to turn that I've found so far. Not that I've tried Hickory or Pecan yet, but I imagine I'll get hold of some before too long...
I turned some English Ivy the other night just to see what it was like.... The first green stuff I've turned. Fun to see the shavings fly off, but I didn't like getting wet!
I think you ought to try all of your available wood out... You'll learn a lot about wood in the process. Just because White Oak is hard to turn doesn't mean you can't learn from the experience. And just because a skew is difficult to master doesn't mean you should never pick it up...
Hope this helps...