The new in-line edit functionality of JIRA 5.1 significantly aggravates the existing problem of JIRA generating too much email for small changes to tickets. JIRA should intelligently group changes made to an issue over a short period of time into a single notification.
Ideally JIRA would attempt to notice when a user has left a page and know that it is safe to send those notifications immediately. Otherwise a time limit would likely have to be used to determine when the user is "done." The time limit should be carefully balanced so as not to incur significant unnecessary delays in delivering the notification message. I would suggest that 1-2 minutes is probably in the right range. Alternatively there could be a "dirty" indicator on the page and a button available that the user could click to generate the notification event immediately.