I have a customer who wants to send a hashed link in an e-mail reply (or anything else that will do the trick) to a participant so that they can cancel their registration for an event without having to phone or send an e-mail. We use profiles in the Events. We use CivicRM 4.6.12
I don't think This functionality exists yet.
I know this is over a year old, but I think it deserves an update. In 4.7, functionality has been added to allow for user self-service cancelation. When enabled for an Event (on the online registration tab), it sends a cancel or transfer link in the confirmation email. See https://issues.civicrm.org/jira/browse/CRM-16761