I recently upgraded to 1.1, this behavior didn't start as soon as the upgrade, however I can't fully rule out that is part of the problem. As I am not fully versed on tomcat and java and ActiveMQ so I have attached an excerpt from the logs (/opt/oncall/logs/oncall.2013-10-07.log) from the time swac stopped polling the email box that we direct the alerts to. All I can get out of it is that the email poller failed.
Recently the exchange admins did make a change that buggerd IMAP, that was corrected and emails resumed momentarily (for about 6 hours). Not sure if it helps
The email poller is failing. Try running through the first part of the getting started wizard to test the email settings.