What is the starting point for Core Data in order to get involved quickly? Any useful link, blog or book or other resourse?
I did start with Apple's doc which is clear and complete.
I'm quite sure there is a tutorial over there.
Core Data is not iPhone only, but i-phone specific elements are clearly indicated.
Besides the Apple documentation, you will find extremely useful the following book:
Core Data, by Marcus Zarra.
You might be interested in video of the Core Data class from my Advanced iPhone Development course, which is available for free on iTunes U. I walk through Core Data and how to use it in an iPhone application.
If you log in to the iPhone Developer Program site, you have access to a series of videos for free, among which is the session "Working with Core Data" (in the Advanced Videos section).
For more advanced information, the WWDC 2010 session videos have the sessions 137 "Optimizing Core Data Performance on iPhone OS" and 118 "Mastering Core Data".
Marcus Zarra's book is awesome and I love it, but I got started with More iPhone 3 Development from APress. A few chapters in the book walk through creating a Core-Data based app on the iPhone, and the code is actually pretty usable in further projects.