I guess the price of free is pretty attractive, because the iPhone SDK has already seen somewhere in the neighborhood of 100,000 downloads. As you know, the SDK is free to download, but Apple charges you an annual fee to have your SDK-developed applications show up in the iTunes App Store, which is really the only way to get your custom iPhone application out to the masses.
The SDK has only been available for about a week. Interestingly, it’s unlike Apple to include quotes from executives of other companies in their press releases, but that’s exactly what they’ve done to announce the high number of SDK downloads. It’s almost as if they wanted to support third-party development all along.
Among the companies cited in the release are Namco, NetSuite, Intuit, Rocket Mobile, PopCap, Six Apart, and THQ.