OF without synch is a partial solution, what makes it work for me is the multi-platform approach.
I don't (currently) have anything that is client confidential on OF, just my own notes and ideas, so sync via the omni server doesn't present a problem for me at the moment - I can see that it could in the future - even just from a 'due diligence' standpoint.
If I had the option of entering an encryption key (which I would have to do on all three devices - OF, iPad & Iphone) or leaving my data un-encrypted, I would choose the encryption option.
As OF files are zipped, how complex would it be to encrypt prior to sync?
The user could choose the complexity of the key from none(default) to a 256 byte complex alphanumeric with symbols (or something in between).
That said, there are some issues with encryption with zip files.
http://en.wikipedia.org/wiki/Zip_(fi...at)#Encryption
I think that it is almost impossible these days to protect information from someone determined to get my specific data - what is appropriate is to make it harder for my data to be gathered as part of a wider sweep or harvest.
If the omni server got hacked and everybody's files copied - any criminal is likely to go through the plain text ones first leaving encrypted ones to the end. Assuming no security flaws that entirely defeat the key (Think WPA) if I have a very long and complex encryption key my data will be at the end of the list.
In summary:
+1 on the list for encryption of synched data.