My father, brother, and I have used walkie talkies for all 10 years I have been deer hunting. It can be a big help. There are three of us on an 80 acre plot that contains multiple tree lines, pasture grass, a pond, and about 25+ acres of standing timber. We even really have one stand, where I killed my big buck last year, that is setup mainly as a watchtower type thing. It is the tallest stand we have, probably only about 15-18 feet, but on a hill that overlooks almost the whole 80 acres. Usually my father will sit in that stand, but I sat in it quite a bit this year.
We will radio one another if we see a deer that is going over a hill, or behind a tree line and is out of sight of another one of us. My brother almost got about a 110-120 inch 8 pointer this year that I passed on in hopes it would get to him. I radioed him once the deer was far enough away and told him it was coming up behind him. However, it snuck into some tall thickey behind him and he never saw it. Then when he eventually came back over the radio to tell us he never saw it, we told him to do a couple grunts and see if you can draw him in. Well, he grunted, and nothing, then brought up the bino's to check the thicket closer and the he caught a glimpse of the buck as it saw him bring up the bino's and bolted. It would have been the biggest buck he has ever shot.
They are a very good idea in terms of safety, especially when it is so icy like it is here currently. We each all take off in different directions on our way to the icy ladder stands and as soon as each of us get into the stands and settled we always radio back and tell the rest of the group that we are up, and safe. Then when we plan on getting down we let everyone else know. That way, if we don't hear from that person again for like 5 or so minutes, we start heading in that directions. However, usually if someone is talking to you and you can't talk because a deer is in the area, we usually give a few quick beeps back, just to let them know we hear them and we got something going on.

Its legal here in Illinois and if it wasn't we would probably at least call each other on our cell phones for getting in/out of the stands. I know this is a little lengthy, but I have been using these things for a decade know and I love them.