John, a Jittepak does exist, however, it is owned by a Jitterbit customer.
It does the following:
1. Every 20 minutes (schedule can be configured) Jitterbit checks Salesforce.com for cases that are a certain type (in this customer's case the type is "Bug").
2. It creates a bug in Bugzilla and then updates Salesforce.com with the Bugzilla BugId. We created a custom field in cases for Bugzilla BugID.
Its very straight forward and we would be glad to work with you to deploy something similar in your environment.
If you would like to utilize our services for this please contact firstname.lastname@example.org