Remote encrypted backup solutions such as Carbonite rely on proprietary software both on the client and server side.

An open modular alternative sounds appealing. Providers such has geneticmail.com offer file hosting with webdav which should be a good and open backend.

!!! Modular approach with filesystem

One way to achieve remote encrypted backup with the encryption happening on the client is to:
* export remote storage as webdav
* mount the remote storage locally
* mount an ecryptfs filesystem on top of the local mount of webdav
* rsync the data from the local storage to the ecryptfs filesystem

This should be fine with Linux but requires Operating System and low level features. So it would be a problem on Windows. 

[{GraphViz title='Encrypted backup3' filter='dot' imap='false'

node [shape=box];

$(nodeAttributes)
"Local Storage"--"Backup Program"
"Backup Program"--"Ecryptfs view of medium"
"Remote storage"--"Remote webdav server"
"Remote webdav server"--"Webdav mount"
"Ecryptfs view of medium"--"Webdav mount"

}]

!!! Recoding ecryptfs in Java

Ecryptfs in java
The idea is to use Java to implement access methods for ecryptfs and use that to implement a small webdav server of it.
That would allow windows and mac users to access ecryptfs data without root access.
That could be cool for a USB key.
Ecryptfs backend for a wiki? There is already a kernel implementation of ecryptfs and the wiki can use files.
Ecryptfs uses openPGP essentially. So the relevant APIs should be in Java.