Using the webform_confirm_email module you can configure webforms to require a double-optin. This way users will have to confirm their email addresses which is handy if you want to use webforms to subscribe people to an email list or use webforms for online actions such as petitions.
I've collected the patches available, improved some functionality and fixed a few small glitches. Additionially I documented some existing functions in the code.
You can find the sandbox project on drupal.org: http://drupal.org/sandbox/matthias_mo/1883024