The new Defect Tracking Gateway plugin for JIRA provides a robust, scalable integration between Perforce and JIRA. Issues in JIRA are replicated to Perforce as jobs, and job updates in Perforce can be sent back to JIRA. The DTG can be configured to send a selection of fields and translate field values between JIRA and Perforce. Fields can be replicated from JIRA to Perforce, from Perforce to JIRA, or in both directions.
I recently wrote a guest post on Atlassian's blog describing the new integration. Check it out!