I could not run any SVN commands using Subversive (clean, update, etc) with Eclipse Version: 3.7.2, Build id: M20120208-0800. It simply hangs with the command "Secure Storage Initialization". After this, I cannot cancel the operation or close eclipse.
The answer to my problem was that the file in %USERPROFILE%\.eclipse\org.eclipse.equinox.security\secure_storage
had either become corrupted or one of the key-value pairs was causing the failure. I moved the file out of the directory, restarted Eclipse, and everything is working fine, again.
I hate to post a question with an answer, but I couldn't find anything on the web that matched my problem so I thought it might help others.