Edit: the rest of this comment is a misconception on my part. I agree with you completely, except that now you can use a smaller, cheaper thumb drive than you

Edit: the rest of this comment is a misconception on my part. I agree with you completely, except that now you can use a smaller, cheaper thumb drive than you could before (though arguably bandwidth limits effect the same result). If you're dropboxing large files, using a lookaside cache means that you can greatly reduce latencies and often improve throughput (assuming you're not on 1 or 10 gigabit directly to the dropbox servers). But I doubt the dropbox servers themselves support this kind of functionality. More likely is that you can move your files to various disconnected computers more easily and automatically without dealing with manually pushing them around from dropbox folders to portable drives.