Hi, out award winning add-on Bug Watcher Notifications has just received this feature.

You can opt for receiving notifications if changes are made to linked issues or sub-tasks of an issue you are watching. Notifications may come in-app or in email and will not violate security rules. This is how it works.

This is an extension of functionality described in JRA-8505. Consolidating discussion on that issue.

A must have feature for enterprises!

We especially have this need / use-case for linking issues across different projects. For example, linking issues between a "Customer Support" project and a product/app project.

My company has been using Jira since version 3.x and just recently upgraded to version 6.1
We had hoped more powerful issue-linking logic (detect state change in either linked issue, customize notification triggers on state-change) was available.

We use a custom subtask to record specific instances of a customer reporting a bug (we call them customer reports), so we might have an issue with 20+ customer reports associated with it. Being notified of these kinds of subtasks being added to an issue would be tremendously valuable to us so that we can spot issues in our system that are getting reported by many customers and can reexamine them. Voting won't work for us in this instance, as external customers do not have access to our issue tracking system (by design), and support engineers need to be able to attach these additional customer reports to each issue and somehow have the customer report count for the overall issue be incremented.

JIRA 4.4 also still does not send out notifications upon link creation (with or without comments)...

We are evaluating Jira in our company (as a Bugzilla replacement), and this is a show stopper. This is such an obvious requirement for a bug tracking system (notifications on linking) that it should really be treated as a bug. Since this issue has been open for 5 years we are now looking into other products, as we don't expect this to be fixed any time soon.

In my organization we use linking also - we deal with distributed organization where the are dependencies between artifacts provided by various project development teams.
We also use JIRA for planning (GH) and the links (depends on / block) ensure the overall consistent planning and tracking of the deadlines.
This notification is really important (especially that we moved from Bugzilla recently and now miss that piece).

We use linking extensively as well: Key Account Managers have a project pr. customer, supporters have a support entry project and both will be linking issues to issues in the Dev Team project (the links can be of many different types: depends on, requires, continues etc.). They want to be notified automatically when there is any update on the linked Dev Team issue. This is an essential feature to have for the intended flow between internal departments to work.

copied from http://jira.atlassian.com/browse/JRA-19755
Description:

Fore example, when issues are linked by Blocker link, for developer waiting for blocking issue resolved would be a good feature.
Having got such notification (s)he can start working on the issue.