I ordered one for about thirteen dollars when Valve had that sale about a month ago and started using it yesterday for the first time.
The camera movement doesn't seem useful. I already have a keyboard and mouse on my coffee table, so having a keyboard and mouse-like experience in front of the TV is sort of wasted for me. It just seems pointless controlling the camera with a swipe when you have none of the range a mouse pad and wrist/forearm provide. Thumbs suck for this. A mouse is great for aiming and a control stick can be adequate depending on the game, but combining both seems like a bad idea.
The face button placement is awkward. They're also small and too close together.
I do like the buttons on the back, but I haven't used them for anything yet.