Can Webforms include the URL they were submitted from in their emails? I have a bunch of webforms in blocks on taxonomy pages.
It would be helpful for the recipient of the resulting emails to know what taxonomy page the user was on at the time they wrote their query.
Do I use the %get token in a hidden field? And if so then what [key] value returns the full (pathauto) url?
Webforms can only use %get[key] and %post[key] for non-authenticated users.
You can achieve this by using the %server token as the value of the hidden field. To be more precise http://%server[SERVER_NAME]%server[REQUEST_URI] should get you the full url (path alias is also preserved). For a complete list of options that can be used with the %server token check out the manual.

UPDATE:

The %server token only works for authenticated users since Webform version 2.8 due to potential security/privacy issues with some values. Since you only need the url in e-mails a better solution should actually be to put a appropriately themed version of &lt;?php print url($_GET['q'], array('absolute' =&gt; TRUE)); ?&gt; inside your copy of webform-mail.tpl.php file (or webform-mail-[node id here].tpl.php).