Like me, if you were one of those people who just got the Core Xbox 360 console, and don't have any hard drive space, then this is the thing you need. I started out with a 64MB Memory Card when I first acquired my 360, but as I have recently been in the process of upgrading to Xbox Live, then I quickly found out that I needed 124 MB of space just to connect - which is basically double what I had available to me with the 64MB Memory Unit.
So I was faced with a choice, just buy a Premium Xbox for £180, or buy one of these for £25. i think it's safe to say which was the safer and cheaper option.
Buying this product has allowed me a lot for flexibility with my gaming, I've connected to Xbox Live now, and have plenty of space for Save Games and other stuff, you can even download a couple songs or two. Just for fun.
Basically, if you need it, buy it. It's what you need for a Core System and Xbox Live. If you don't need it, I recommend Call of Duty: World at War, Fifa 09 or Gears of War 2 this christmas.