When I worked the animal shelter, we used these all the time. I bought one to use on my collie and one for the cats through e-bay for half the cost. They are well worth the cost even at full price.
Just brushed my collie out a week or so ago and had a plastic bag full of hair. Mind you his hair is long. I then used it on the short haired dog who didn't look like he needed it and lo and behold I got a bag out of him too. This goes down to the skin and pulls out the dead hair that is the stuff you find all over your house.
Love theses things. Highly recommend them. Make sure you follow the instructions tho.
I will start another post about a product I use in conjunction with this so as not to hi-jack this post.