Treating the ceiling and floor, who else has had great results?

As someone who has had to design spaces specifically for acoustical concerns, carpeting/rugs can have a negligible effect on acoustics in general-use settings like homes and office spaces. Carpet can deaden foot traffic noise and high frequencies but as far as helping to tune a room for mid-range and low-end frequencies for audio enjoyment, it's not much help. Of course, the carpet/rug salesman will tell you their product will solve all your acoustical issues but caveat emptor. 

Floor treatments can add warmth and visual softness to a space if you want to make it more liveable and aesthetically pleasing. Ceiling and wall treatments are the most effective surfaces to look at.

In my future listening den, I plan to take room measurements after I have a semblance of furnishings, final finishes, and the built-in bookshelves are filled up because I don't intend to build a listening box with nothing in it but a chair. 

Depending on how tech-savvy you are, you could try free software out there to build a 3D simulation of your room and then listen to it virtually to see how it may sound with different treatments or hire professional services to do that for you.

If I were designing a custom listening space for a client and they have top-end hi-fi gear and want a truly neutral room, then I would recommend hiring an acoustician to assist in designing the right room treatments and dialing in the correct dimensions for a room. 

@kodak805

It’s important to read the whole article. I’ve never claimed a rug was a solution to everything. If you’ve read my posts on acoustics I often talk about having a minimum critical mass before room treatments become audible, including first reflection points. That still applies here.

Darko’s article doesn’t say rugs aren’t helpful, but that they are limited in effectiveness. That’s different. Also, the point I wanted to say here was a little different and dealing with a small overlooked corner of the room behind the speakers. Fortunately I’m not asking anyone to spend money. Throw a rug or blanket behind the speakers and see if you hear a worthwhile improvement. If so, maybe get a panel for that area.

Specifically Darko does not say "don't put a rug on your floor it's useless."  He only points out how limited its effect it is in light of other treatments.   You'd be foolish to NOT put a rug down if you have a bare wooden floor.

Carpet can deaden foot traffic noise and high frequencies but as far as helping to tune a room for mid-range and low-end frequencies for audio enjoyment, it's not much help.

Per square foot, carpets are far less effective than dedicated acoustical panels, but even if we say it's "only" effective above 1 kHz, that's a good thing, especially when the floor is a glaring first reflection point and should not be neglected. 

Still, the overall tonal balance of a room, and even your ability to hear if a carpet is there or not will be determined by everything else.

I'm not here selling rugs.  I'm suggesting if you haven't tried treating the floor behind and between your speakers, for some this can be good.  Also, not here to debate the point forever.  Just try it and if you like it do something more.  

One benefit of tall, narrow dipole planar loudspeakers is no ceiling reflections. And very little sidewall. But of course then there is the 50% backwave to deal with.