Just something short and might save some people (including me!) some headaches. If you are getting similar errors like the ones below:

INFO | jvm 1 | 2008/08/24 12:31:43 | java.lang.Exception: DEBUG ONLY: Overdue resource check-out stack trace.
INFO | jvm 1 | 2008/08/24 12:31:50 | 2008-08-24 12:31:50,448 [Thread-15] (NewPooledConnection.java:425) WARN – [c3p0] A PooledConnection that has already signalled a Connection error is still in use!
INFO | jvm 1 | 2008/08/24 12:31:50 | 2008-08-24 12:31:50,448 [Thread-15] (NewPooledConnection.java:426) WARN – [c3p0] Another error has occurred [ org.postgresql.util.PSQLException: An I/O error occured while sending to the backend. ] which will not be reported to listeners!
INFO | jvm 1 | 2008/08/24 12:31:50 | org.postgresql.util.PSQLException: An I/O error occured while sending to the backend.

Be sure to go through your code and ensure you are closing all your Hibernate sessions – eg. myDao.getSession().close(). I missed one, and it was causing me a lot of headaches!