The post on updating resources in ADO.NET Data Services has gone up on the Project Astoria blog.
One thing worth calling out that may not be immediately obvious is that while this is very straightforward to implement this is you have an object model that implements change tracking (because your 'cookie' can be your actual instance), this isn't the only way. You could also implement this by capturing the initial query in the cookie, and then appending all the described changes into some sort of change log. At "SaveChanges" time, you have all the information that the system was able to provide as to what changes the client was requesting, and you can persist them in whatever manner is more appropriate.
Of course if you're using the ADO.NET Entity Framework, you get everything for free - no need to worry about this.
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