I use Apple's iCal application for my calendaring needs. It has the ability to subscribe to a published calendar (via HTTP). This published calendar appears as a separate calendar entity within iCal and is a read-only view of the data. iCal seems to support both events (including alarms) and tasks (todos; along with due dates) from a subscribed calendar.

I envision JIRA providing a calendar feed that I could subscribe to that would show tasks that I need to attend to (bugs, issues, tasks, etc.) as well as upcoming due dates, like releases. I think this feed could be fed from the same information that drives the current dashboard view. I've come to use iCal to see all kinds of information on a single calendar view, and, coupled with iSync, can also carry this calendar on my Palm.