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

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.

GIK absorbers on ceiling and side walls along with a good thick cut pile wool rug with pad. Vicoustic combination absorber/diffusers in the front corners, on the front wall, and on the side walls. In the middle of the front wall is a large Vicoustics wooden diffuser ensemble. There are also Vicoustic diffusers on the ceiling. Behind the listening position is another mix of absorption and diffusion devices. Probably 50/50 absorption/diffusion overall.

My recollection is that you want to treat roughly 30% to 40% of the room's surfaces. 

This may not be an option for some, but Armstrong makes suspended acoustic ceiling tiles. I used these in my sound room and they worked wonderfully to mitigate an upper midrange glare. They are also inexpensive and look good.