What can be done with 'PermGen out of space' exception in Tomcat-Spring-Hibernate web application?

Question

We have an web application that uses Spring-Hibernate to persist registered users data in Oracle database. The application works fine in development environment, but when we

Answer 1

All responses here relates to PermGen problem that happens because of several restarts of web-app, but in this case the problem already happens on first deployment after tomcat restart, so it can't be the problem of ClassLoader's references or commons-logging.