At last, I was able to get the svn+ssh protocol to work from both IntelliJ IDEA (Irida #3200) and Eclipse (3.1M4), using a private key! Here's how to do it:

For IntelliJ IDEA

• Start by downloading the latest javasvn.jar from the TMate JavaSVN web site. You need version 0.8.0 or later (I've used 0.8.0). The reason is that there is a new property named javasvn.ssh2.key that has been added as a hack for getting the Subclipse plugin for Eclipse to work with svn+ssh... Drop the jar in [IDEAHOME]/plugins/svn4idea/lib , replacing the existing jar of the same name there.
• Modify the [IDEAHOME]/bin/idea.bat file to add the javasvn.ssh2.key system property: IF "%IDEA_JVM_ARGS%" == "" set IDEA_JVM_ARGS= [...] -Djavasvn.ssh2.key=/path/to/your/private/key .
• Make sure you use an openSSH-compatible private key. The Putty format is NOT supported by JSch. If you have a Putty private key, use Puttygen to export it as an OpenSSH key.
• Make you sure you specify a valid username in the IDEA subversion setting, leaving the password field blank.

For Eclipse

• Install Subclipse using the provided Eclipse update site
• Install the JavaSVN Subclipse Extension, also using the provided Eclipse update site
• Modify the way you start Eclipse as mentioned on the JavaSVN Subclipse Extension web page
• Go the SVN Repository Exploring perspective, right-click on your SVN Repository, click on "properties" and make sure you enter a valid username (leave the password blank).

Enjoy! That should please all the Codehaus hausmates... :-)