IT WORKS!
Our house was built in the 70's.  The floors upstair squeaked with every step, and it became unbearable.  A handyman told us he'd have to lift up the carpet to fix the squeaky floors, and gave us an expensive quote for the job.  We searched around and found a youtube video of this product.  We were skeptical at first, but at around $43, S & H included, we figured we should give it a try.  My husband struggled at first to find the joists, and ended up with some small holes in the carpet.  We thought the damage is permanent, but after some vacuuming and steaming, the carpet is whole again.  Though at some spots we could still hear a light squeak, overall it has improved 90% for us.  We ran out of the first pack and had to purchase another one.  The S & H fee is outrageous, but they ship fast and we received the product in less than 5 days after we purchased it.  Overall, we spent less than $100 for 2 kits, and we were able to fix the entire floor upstairs.  Our stairway is also squeaky, but we have no idea how to fix it.  Hopefully someone can give us some tips.
Rating: 5 stars