Probably easier'n every other wood, soft or hard. Planing poplar doesn't even count as practicing.
I didn't raise the S2S/S4S HD ripoff question because I figured the OP was in the same situation I used to be in. I made stuff out of poplar because Lowe's was the only place I knew to get wood, and it was all I could afford at their exorbitant prices. I made the best of it.
Once I discovered a place to buy real wood, I've never bought poplar there, even though it's cheap. For what I was paying for S4S poplar (with wider than 3" boards done as glue-ups, no less) I can afford a similar quantity of walnut. Let's see, walnut is available. What wood do I want? Duhhhhhhh. :)
It hasn't saved me a dime finding a cheaper source of wood. :)
I really need to look elsewhere still, but I guess I don't care enough to drive out to some yonder (Bedford, say) or fool with mail ordering or whatever. I don't think I would build much more, or much bigger stuff than I do if I had a whole tree cut up and stacked somewhere, and somewhere to stack a whole tree. I have a little bitty shop, and I favor either purely utilitarian projects made out of whatever crap salvage I can scrounge (my Frankenstein music stand, or trebuchet, say) or else I do small projects in (predominantly) walnut that take me weeks or months to complete.
I'm not really aiming to do things faster, or put more wood through the shop just to be doing things in a hurry, and I don't mind doing a little bit to ensure I can continue to go buy wood on the other side of town whenever I want to, even if their prices are high.