Shameless plug: I've implemented something similar in the past, but with the addition of client-side encryption. I've been using it for some time without problems.
At a first glance at the design docs here, the present project looks more sophisticated in terms of syncing. I'm just using local file operations and hoping for dropbox to do its stuff :)
I think the problem with your analogy is that it doesn't include the measurement basis. Consider polarization of a photon: you can either distinguish between horizontal or vertical polarization with a measurement, so your basis looks like a "+". Or you can distinguish between diagonal polarizaitons, so your basis looks like an "X".
Now, considering two photons, you don't know which basis Alice or Bob will choose in advance. If you just say "the photon is polarized horizontally", then their outcomes will be random if they measure in the "X" basis. If you include so-called "hidden variables" for all possible measurements, then you're basically at Einstein's idea.
(I've simplified some things above, so please don't quote me on it ;)
Shameless plug: If you want the data in dropbox encrypted, try https://github.com/lucas-clemente/git-cr :) I think I've also solved most of the concurrency problems, but haven't tested it yet.
At a first glance at the design docs here, the present project looks more sophisticated in terms of syncing. I'm just using local file operations and hoping for dropbox to do its stuff :)
https://github.com/lucas-clemente/git-cr