Add ability to subscribe to issues

Would it be possible to add the ability to subscribe to issues for a given project, much like you can with project issue tracker? I am currently evaluating whether to use project issue tracker or case tracker for a customer support site and with the exception of the subsribe function, case tracker seems far better suited to this.

The ideal situtaion would allow someone to subscribe to a project, thus receiving an email notification for all new and updated issues on that project.

Thanks.