For those with big screen digital televisions out there you won't want to be without one. For everyone else, don't read further.
It really is somewhat difficult to write up a real review for a piece of equipment like this one since the answer is somewhat black and white with only minor shades of gray. If you have a big screen digital TV you'll likely already appreciate the necessity of the proper cables to maximize the appearance of images on your investment. If you don't have a television like this you wouldn't really have a reason to buy this cable and you probably wouldn't even have inputs for it.
Anyway, now with that out of the way lets get on to the specifics. One very important thing to remember with this cable is that it will ONLY provide you with video, you will actually still need a plain old Nintendo AV cable (the same one they've been using for a while now) to get your stereo sound outputs (hopefully for your surround sound receiver). It was because of this way of hooking things up that I was so easily able to contrast the look of the plain cable with the component one since I could switch back and forth between them.
First and foremost in terms of picture quality the difference is predictably quite noticeable even to eyes that aren't picky. The standard AV cable's video display had a pretty consistent flicker visible, the colors were much more muted, and there was more of a blur to everything on-screen. With the component cable the video quality was very high, the colors seemed to jump from the screen, and for the most part even the interlaced display looked excellent.
This brings us to about the only other major point, the progressive scan quality. All that can be said is that there is some difference, most predictably with the letters looking a bit cleaner. Surprisingly though, with the exception of an odd detail here or there it was hard to discern many other visual differences between interlaced and progressive.
In the end, as noted, this review is much more of a quick summary than something full-blown since people with high end equipment won't hesitate to pick up the best cables they can find. That said, take some reassurance that from a comparison with standard AV cable there is a very noticeable difference and your money will be well-spent.