The iphone SDK notes

Introduction

Apple's SDK blows open the process of creating native apps for the iPhone by letting most any would-be coder get started.

Developers

According to iPhoneDevCamp co-founder Raven Zachary, "The fear [in the development community] today was that Apple was going to constrain the ability for third-party developers to distribute apps, in the same way they did with the iPod games market." Developers can sign up and download the SDK for free, which in turn allows Apple to reach out to a wider cross-section of would-be coders than they might have otherwise.reaction has been almost universally positive to Apple's SDK plans.
Developers had feared worse outcomes, such as having to submit their source code to Apple, and seemed willing to let Apple take a piece of their revenue and be the exclusive distributor for iPhone applications in exchange for getting a crack at the technology.

you're not going to be able to use anything other than Apple's official APIs (application programming interfaces), notes Ken Aspeslagh (via Daring Fireball). This isn't much of a shock, but it means that a lot of techniques learned developing unofficial iPhone apps will probably not work with the official SDK.

Multiprocessing problem

Apple's SDK documentation (embedded in the TechCrunch post) points out that the iPhone can only display a single application screen at a time, and urges prospective developers to spend a lot of time designing an application that can handle quick stops and starts. "In other words, users should not feel that leaving your iPhone application and returning to it later is any more difficult than switching among applications on a computer."
iPhone might not be able to support the processing demands required by multitasking, but plenty of other phones seem to be able to juggle more than one application at a time. I wonder whether future Apple-developed iPhone applications--like, say an iPhone version of iChat--will be subject to the same restrictions.

Intel's upcoming mobile processors

One interesting passage in the iPhone SDK documentation should give Intel something to think about. "If you have an existing computer application, don't port it to iPhone OS. People use iPhone OS-based devices very differently than they use desktop and laptop computers, and they have very different expectations for the user experience."

Intel has been pitching its upcoming lineup of x86-based Silverthorne and Moorestown processors as ideal for the next generation of mobile devices, because they can run any type of software that you can currently run on a PC. The chipmaker has a point in that if you're already familiar with x86 development process, you might find a Silverthorne chip an easier target than an ARM-based chip. But all those Mac and PC software developers will have to bring a totally different mindset to mobile development anyway. Those developers who have been doing this type of development already could have a substantial edge.

Sources

The iPhone SDK: The day after CNET News.com
Apple's iPhone SDK Strategy Both Promotes and Stifles Innovation Washington Post