It is pretty fricking annoying to have to register for both your message board and for JIRA to put a bug in.
Have to say, that with JIRA account you’ll be able to watch and vote only. To add bugs one will need special permissions turned on by JiveSoftware team. Probably there was some point t not to integrate JIRA and JiveForums (before Clearspace appeared), especially that JIRA is not the JiveSoftware product. But you can always use the same login and pass for both message board and JIRA.