Hi Biggerplay,
we are currently working on a full service for challenges, leaderboards and achievements, synchronized across multiple devices and working across platforms. This service will be available in Q2 2013, and earlier for our Pro users who have access to daily builds. The service also contains a backend integration for local data with synchronized storage (answering your second question). In the meantime, you can use the Storage element for a key/value store and save your local scores or other permanent data locally with it – the synchronized storage will have the same API, with the addition that your data is synched automatically, so there will be no overhead for you when switching to the cloud synched storage.
Cheers, Chris