Because I wear a womens US size 8.5, I first ordered these in a size 9. Ecstatic when they arrived, I slipped them on and immediately said, "uh oh." They would fit only with one pair of thin socks.

I contacted company, who suggested that I wear them around the house (can't return them if they're dirty!) for a couple of hours. After clomping back and forth and finally succumbing to half-lying on the couch with my feet on the floor, I had to conclude that, although they were ever so slightly roomier, it still wasn't enough.

I sent them back and exchanged them for a size 10, which is perfect. My feet are never pinched into dress shoes; ergo, they may be slightly wider than average, but not by much. The size 10 gives my toes room to wiggle and spread apart while wearing a pair of liner socks and a thick pair of insulated socks. Yet, my feet don't slip around in them.

As for the other aspects:

These are definitely large, clunky boots. However, they need to be, to keep the cold from seeping in through the sole, as they did with my Sorel Caribous.

They slip on and off like a dream without having to adjust the clips. While the clips are better than laces, they don't quite match the "easy-to-fasten-while wearing-mittens" description that's given on the web site. Nevertheless, I haven't even bothered to tighten them yet. Unless I'm out in deep snow, I won't need to make any adjustments, as they stay on quite comfortably.

My calves are fairly thin and the liner is comfortably cushiony and cozy, but not tight, while I have a pair of baggy jeans tucked into them. Enfolds my feet and ankles like a hug from an ample grandma.  At 5' 7", the boots come 3/4 of the way to my knee.

The reflective piping is a nice touch for visibility to others at night.

Rated at 128 degrees below 0, I can't imagine these being tested under those conditions! Still, for people with normal circulation these should be more than adequate. My feet are always cold.  Even wearing the boots in a 62 degree house for over an hour, these tootsies didn't break a sweat. I've worn them in a 80 degree greenhouse all day and found them merely "very warm." Still, although I haven't yet been able to test these in the single digits for an entire work day, I can say that standing outside for an hour at a temp of 4 degrees, my feet were fine. Not hot, but definitely warm enough. In the Sorel's, my toes would be numb and stinging in under 5 minutes.

As long as my feet are warm when I put them on, they seem to hold most of the heat. Putting the boots on the boot dryer increases the heat retention even more! ;-)

I'm delighted with them.

Update: 2/26/13  After weeks of wearing, the liner has compressed a little more, giving my feet even more space. Nevertheless, I'm still very happy with them and infinitely prefer something slightly larger to slightly smaller. Also, one reviewer commented on the problem of one's heel slipping up and down while walking due to the inflexibility of the boot. This is true and there is nothing to be done about it. However, I don't find it bothersome. Then again, I'm not going on long hikes in them, either.

Update 2/9/14  I'm still happy with them. A few things to mention:
  - With this winter's below zero temps, I was glad that I'd ordered a larger size. I'm outdoors a lot and am regularly wearing a pair of acrylic knee socks, heavy wool hiking socks and a final pair of thick Merino wool kneesocks over the top. My feet, most of the time, are quite toasty. However,  on those days when the temperature was no higher than 2  to 5 degrees, if I wasn't moving, my toes got cool after a couple of hours.

  -  These boots soften and spread out a lot. So, width-wise, they're a lot wider than when I first bought them. Saw a new pair and couldn't believe how much narrower and higher they were! Just be prepared. My feet, even with all of the socks, still have room to wiggle. However, I'm not noticing any uncomfortable sliding. I have too much sock padding for blisters. ;-)

  -  These really have been getting a workout from me this year. Started wearing them in November and haven't been out of them since. Five to six days a week, all day long, clomping through fields, with snow and without. I'm thankful for them.  And, because each boot weighs a little over 2 lbs (that Amazon shipping weight is incorrect!), my legs are getting stronger. ;-)

In short, my formerly frozen feet are most grateful.