As a .Net developer I always dreamed for the possibility to develop with my existing skills (c#) applications for the Iphone.
Both programs require a Mac and the Iph
There are numerous ways to get on the device. Apple has stated in the SDK license that the only approved way to get on the device is via C, C++, ObjectiveC, and Javascript.
It appears at this point in time that apps built on MonoTouch and Appcelerator Titanium are being accepted into the App Store. Thanks to the license change, there is much fear, uncertainty and doubt on this subject. Apple has scared everyone not doing ObjectiveC.
I would suggest that you do whatever makes the most sense for you as a developer. If you know C# and .NET, you should go with MonoTouch. If you know ObjectiveC or the Mac platform, ObjectiveC is probably the way to go. If you know X and it's on the iPhone, well, X is where I would suggest looking first.