Rules help: After updating existing content
For your task you need site:current-user token which corresponds to $GLOBALS['user'] (global $user) object.


  I'm not sure how reliable this is when multiple users are logged in to the system?


Webserver creates new PHP thread (or process) for each request so there are no sharing variables between requests.global $user variable is initialized by Drupal on every request.

When you have just updated a node you can use global $user to know who updated this node. At any time after updating you can get that user id from revision ($node-&gt;revision_uid).