I've been hitting garage sales for about 3 years now looking for old artificial trees and have collected several for next to nothing. Like Nwbuck I use them mostly for building groung blinds. I also use the 12' hog fence panel, with the 6" square openings. I cut a couple of the openings out, bend the panel into a round shape with a door opening in the back and then attach the Christmas tree limbs to it by bending the end of the twisted wire in a hook and simply hang them on the panel. I mix in other brush and hand a piece of camo blind material over the door opening. Of course they are anything but mobile but I set them up in turkey struting areas and leave them year round. I shot my first Gobbler with a bow out of one this past spring and had numerous birds and deer less than 10 yards from the blind. It's also been a good place to take my niece and nephew for there annual deer hunting trips. I hope to get a double bull blind soon but these are a cheap way to build a blind.
I've also used the branches on ladder stands to help hide them.I attach them to the stand legs with cable ties. It really breaks up the outline.