Ubuntu to store copies of all users' address books

From experience, I don't recommend it though :-). There's another one-liner that goes 'Ubuntu is African for "person who cannot configure debian'. You have to plan on a spending some time up-front on configuration.

E.g. on Ubuntu, setting automatic updates works out of the box. On Debian, "anacron" isn't part of the default desktop task (only the laptop one). If you turn your computer off to save your electricity bill, it won't pick up the updates at midnight or whenever they are scheduled for. You need "anacron" to catch up on the scheduled task(s) which you "missed" while the computer was turned off.

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Back on-topic... this sounds really ignorant to me. Mozilla have already shown you can do sync with encryption, (it's a labs project called Weave); there's no need to pass the server my personal data in plaintext.