I do not use them. I do not like them, and I worry about torn wings and such. I also see no need for them for *me* but I understand that others swear by them.
I am fairly new to beekeeping, but I am up to 20 hives from the one I started with in March 2012, and I do a fair bit of management to make sure I keep moving honey up and out and brood inwards and down. That being said, I have harvested some 20 gallons of honey this year and only two frames had any brood at all, and that was just some drone cells at the bottom of two frames. If I find brood above the brood chamber, and honey frames starting at the outside of the brood chamber, I move them down if I can, or make sure the brood is in the center and the honey outside. I will also run foundationless frames in between frames with foundation, just to keep them on their toes and to be able to harvest comb honey easily.
I tend to put the frames with new foundation in the brood chamber, and return the drawn-out extracted comb above. Unless it looks like she needs room badly. I have not had them fill the drawn out extracted comb with drone...which I thought certainly would happen. But it didnt. They worked with what I gave them.
That being said, where I am there is honey flow 12 months of the year so I understand my management practices to not apply everywhere.
I have never thought, "wow, a queen excluder would make this easier." And, I do think QEs make it harder on them. I think its hard enough already, but that's me.
I always find fully capped frames (both sides), and they seem pretty clear that they like it on the outsides of the topmost supers, regardless of whether they are mediums or deeps.
My hive called the Tower of Power has 4 mediums on top of a single deep, and she will go up to level 3 to lay, but always in the dead center. There is always honey on the outside of every box, even in the bottom deep....she is a trooper and runs a tight ship of super productive bees!