I have never used it but I just read about cocos2d-android earlier today.
From their site:
cocos2d for Android is a framework for
building 2D games, demos and other
graphical/interactive applications. It
is based on the cocos2d-iphone design:
it uses the same API, but instead of
using objective-c, it uses java.
(here is a link for cocos2d-iphone)
So yeah, I have never used it, and I don't think you will be able to share source files between the 2 platforms because as they mention it uses Java instead of objective-c
It may be possible to create a library that can be used by both platforms, but I am not 100% sure about this. The Android NDK (native development kit) allows you to write some functions in C and C++ and hook into them in an Android application via JNI (Java Native Interface). The latest NDK supports OpenGL ES 2.0 So it may be possible to share code, but I am really not sure.