Here we collected some questions (and answers to them of course) that are not directly answered in the developers' documentation. Answers to such questions can often be found on discussion boards, or not easily found at all.
Yes, you can. You are limited to running the apps in the iPhone simulator, but you can start. Here' a list of what you can and can't do.
Please see the iPhone Developer Center for the complete list of membership benefits.
As stated above, no. There is no technical way* to do that. iPhone and iPod Touch can only run code-signed code. The code must be signed with a certificate acquired from the Apple certification center. Developer Program members can create the certificates in seconds, but those cannot be created otherwise. So, no, it is impossible.
* unless you do some technically difficult, dangerous, and illegal stuff
Core Animation is well integrated with the UIKit framework, so unless you are creating a game you most probably will use it. It has many features, complete and convenient Objective-C interface, and is ready to use. All you have to do is to tell it what kind of animation you want, and it will do the rest. You don't have to draw every frame, you don't even need to create any timers—the framework will do it for you.
The only drawback is performance. Even though it's integrated in the OS, the Core Animation will be slow with hundreds of layers animated. Also, fast creation and distruction of layers (as needed for particle systems, for example) will not work well.
With OpenGL you are responsible for everything and have to handle all drawing and timing. Optimization is also your responsibility. But well optimized, a graphical engine based on OpenGL will work much better with retatively high load.
Also, Core Animation works only with 2D graphics (except for transforms and transitions that have 3D look). OpenGL can handle both 2D and 3D.
Please see Frameworks and classes for common tasks to find the table of frameworks by task along with direct links to their documentation at the ADC website.
It is possible to make a laptop's built-in accelerometer work as the iPhone accelerometer in the simulator. That is you can tilt your Mac, and it will work as if the iPhone was tilted. Please note that the accelerometer in a Mac works differently, and the results will be different from the ones on a real iPhone.
Also, you can use the app accelerometer-simulator to transmit the accelerometer data to your development machine from an iPhone via the UDP protocol over the network. All you have to do is add an include to your project and install an app on the iPhone.
Note that you will have to build and install the transmitter app yourself as a developer—it is not available on the AppStore. This means that you can't use this method if you are not a member of the iPhone Developers Program.