Great to use, especially when a reward is offered, but don't be in a hurry to use it.
Used this to get an optical drive for a discount.  (15% or something, I don't remember exactly.)  While I was quite happy to spend less money, I was quite annoyed when a promised 10-minute turnaround ended up taking 9 hours.  And that's why I rated it less than the full 5 stars.
Rating: 4 stars