To receive notifications of updates on issues meeting a set of criteria (For example, watching the output of a particular user), create an issue filter meeting said criteria and either subscribe to it by mail or add the RSS feed to a newsreader software.
For example, to search a list of issues with the following criteria:
Updated from: -1d (updated within the last 24 hours)
The filter subscription will periodically send a notification reporting the issues assigned to username which have been updated within the last 24 hours. For more information, please refer to: