David Simmons explained how the 'disconnected mode' works today in Entity Framework (and as far as I know, that's the way it will work in the Orcas release).
Basically, there is no disconnected mode. You can create a context and attach objects that you kept somewhere, telling the context if it was added/deleted/modified.
This basically means that if you plan to build a multi-tier application with ADO.NET Orcas in the middle tier, you will need to hack your own change tracking mechanism in the client, send the whole changeset, and apply it in the middle tier. From this point of view, it's a huge step backwards, as that's something we already have with DataSets today.