Cloud-based backup and synchronisation across computers is very practical and very insecure. There are VERY few solutions where the encryption in the client, namely in your own machine, and only encrypted data is seen from outside. Even the service provider cannot decrypt. One such service was (yes: was, not is) Wuala, which for the last year had markedly increased in speed and reliability. Now, after being owned by LaCie, the are shuttering down.

As a replacement I have been testing Tresorit

Looking good so far. Fast, reliable, similar pricing. Written with Qt, giving a good cross-platform GUI experience. A number of caveats:

• The possible character set for filenames is restricted to the Windows set, thus disallowing

" * < > ? \ / | / :

Quite obnoxious if you're used to Mac filename conventions.

In my case, over thousand of files had to be renamed, which was only possible with the help of "A Better Finder Rename"

A plus here: I contacted support, to ask why characters where relevant, given that everything is encrypted anyway. I got a rapid response giving cross-platform synchronisation as explanation, convincing.

• Tresorit follows hard links, thus possibly duplicating your files.

• There is no way (so far?) to filter, that is to remove specific folders, nor remove files based on filename rules from the set.

• As to encryption on you own machine: I rely on the manufacturer here, and do hope some white hat hackers will check on that.

I will add to the above when I learn more, so far I'm only using it for a week.

Interesting comparison here