Let participants confirm registration with one click?
One way to do that would be:

Create a drupal webform where you show the CiviCRM user and the Event and a Submit button that registrates the visitor to the Event.

If you use a checksum token in the link then the person you mail will be shown on that page. 

With a second parameter in the URL, for example "&amp;action=register", you can use Javascript to auto-submit that form.

(Simirarly you can also create a cancel webform + email to send to people who already registered, so you make it easy for them to let you know that they will not be there).