No, it just requires you to trust them to be careful and finish syncing first. And a bit of luck or scheduling to make sure two people don't work on it at the same time.
Think of it like a word document. What happens if you store a word document in there, and multiple people need to edit it? Pretend the fancy-shmancy brand new collaboration features don't exist.
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Alternatively, the upcoming calibre v3 is expected to have read/write capabilities in the server.
Essentially, you will be able to run calibre on one computer and connect to it from other computers as a cloud service. (This is especially interesting to those who have moved over to a Chromebook, I guess.)
Also, collaboration!