If you're used to writing apps in a Windows/Linux world then you probably don't have a ton of experience with objective-c. Apple's main language of choice can be frustrating for a lot of developers, and it can be hard to justify purchasing a Mac solely for developing iPhone apps. Luckily several different projects are starting to come out that allow iPhone development on Windows platforms and in languages other than objective-c.

Flash may not be coming to the iPhone browser any time soon, but Adobe has been putting a lot of effort into proving support for building native iPhone apps using the Adobe Flash Platform. Apple's iPhone developer license forbids using runtimes or JIT compilers alongside apps to run things not written in objective-c, but Adobe has gotten around this by using LLVM to do Ahead-of-Time (AOT) compilation. This should allow apps written in ActionScript 3 to run at/near the speed of a similar app written in objective-c.

CS5 will support iPhone development on all supported platforms (both Windows and Mac).

Adobe Labs - Adobe Flash Professional CS5: Applications for iPhone

Developing for the Apple iPhone using Flash