The undisputed heavyweight champion of BDAs, iTunes demonstrates that if you find an underserved need and build a highly usable interface for that need, the sky is the limit. In this case, Apple is the brand, iPod is the product and iTunes is the BDA.

The application

The good

• When iTunes started, it gained momentum purely because no other company offered a way to create and manage MP3 files so well. I've often thought that if Apple decided to make a similar application around the process of filing and retrieving cooking recipes, they'd take over that industry, too. After all, iTunes isn't a whole lot more than a really nice database with ecommerce attached.
  
• What makes this possible is the desktop. Managing this information online wouldn't work for all kinds of reasons, but on the desktop, Apple is free from the design restraints of HTML and can build an application specifically suited to the needs of the user.
  
• Now that users are trained on Apple's way of managing music files, extending that user experience to ecommerce is seamless. You can fill out the holes in your music library without having to learn anything new. The interface is the same one you've been practicing on with your own files.
  
• Welcome to the desktop portal. As you may have seen, the power of a trained user extends offline to physical products both vertically (iPhone, iPod, AppleTV), and maybe, more amazingly, horizontally across products within the same vertical. For example, for jogging, you can you buy the Nike+ service that tracks your progress with the iPod Nano. But when you want to have TV, movies and music at your disposal, there are color screen models, and you can use them all effortlessly with the same connection cord and interface.
  
• Another amazing result of filling this space with a usable interface is how good the ecommerce can get. The now-vacant Sam Goody in the nearby strip mall attests to the reality behind more than 2 billion song downloads.
  
• And did you notice, no website? Well, you can go to the web for information about iTunes, but you have to download the BDA to buy. I asked if you noticed, because most people don't distinguish between ecommerce through a BDA and a website.
  
  In fact, eMarketer recently reported that women ages 16 to 25 have voted iTunes their No. 5 favorite website, which is a telling statistic for the future of ecommerce and a very important lesson for anyone interested in capturing the attention of such an influential group. These are the household financial managers who will dictate the success of your brand over the next decade.

The bad

• Yes, there are problems with iTunes. First, the restrictions cross the line between business objectives and serving your users well. This "beat me or join me" attitude will almost certainly end up defining iTunes as either a fad or a trend. Remember, iTunes is only a few years old. We may end up looking back on it like synthesizers you wear like a guitar or women's suits with shoulder pads.

What can you take away?

• iTunes really has something for everyone to take away. It demonstrates the BDAs' power to customize an interface completely to your users' needs, as well as the rewards for companies that achieve that level of interface utility.
  
• What need is your brand an extension of? Apple looked into the lives of its target users, found where help was needed and created a way to overcome those obstacles (real or perceived) first. As I mentioned, Nike leveraged the Apple BDA in a partnership, providing its customers hardware and software to complement the way they're already using a product.
  
• Simple ideas are often the best place to start. Apple did it by creating an application to allow its users to track songs. A laundry detergent company can apply that same helpful concept by creating a BDA timer to remind customers when the wash is done, with a click to the web for tips on stain removal. If you're a household product, a desktop "cleaner" tool with your brand could organize the desktop workspace.