It would be a useful feature to be able to set up a regular email to each user giving their list of current open issues; a nag email.
A possible way of doing this would be to have a service than ran regularly (e.g. once a week). This service would trigger a custom event when it fired. That custom event could be used to trigger email sending. Currently it looks like the events can be triggered only on workflow transitions, which means that they require active input from somebody.
I'm aware that each user can set up a filter of their open issues and then subscribe to it; which allows them to get a regular nag email at whatever frequency they choose. That's a good feature. It is, however, voluntary; there's no way (that I know of) of forcing the user to have this subscription. Also, it requires setting up an individual filter and subscription for each user.
If a timer service were available, it could potentially be useful for a number of other events as well as sending regular email.