In Xcode 4, there is a Myproject.entitlements file.
What's it for?
In general, what are the "entitlements"? What are they for?
It's related to iCloud and push notifications (on iOS and Mac OS X) and the App Sandbox feature (in OS X only).
There is more information in Entitlement Key Reference. App Sandbox is documented in App Sandbox Design Guide:
An app that is not sandboxed has access to all user-accessible system resources—including the built-in camera and microphone, network sockets, printing, and most of the file system. If successfully attacked by malicious code, such an app becomes a hostile agent with wide-ranging potential to inflict harm.
When you enable App Sandbox for your app, you remove all but a minimal set of privileges and then deliberately restore them, one-by-one, using entitlements. An entitlement is a key-value pair that identifies a specific capability, such as the capability to open an outbound network socket.