I'd like to think that Rob is giving Kristen a song he wrote just for her. Imagine on Christmas eve, or Christmas morning, when they have a moment to themselves...he whips out the guitar and sings a beautiful love song he wrote just for her. (without laughing...you can do it, Rob! ;) He'd do something like that because he knows it would mean more than any $3 million diamond ever could. ;) I'm sure he'll get her some material presents, too--something he knows that she's had her eye on--but he will probably do something else for her (like write a song;) that has personal meaning just between the two of them.