@willr: There is already this ability. Rather then entering a static email in the from popup select the field you want to send from in the dropdown underneath it
You are using UserForms 0.2 correct?
* Make sure you are using a recent daily build of UserForms (or the trunk version)
* Set up your form with at least 1 EmailField type (not a text field or anything). Save your form
* Go to the Email Recipients tab and you should see 'Send Email From' Dropdown with your email fields, select the field and the from address will now be pulled from this field dynamically.
In the "Add A Email Recipient" popup I can select the email field in the drop down for "Send Email Instead To". So if I have an email field I can select this and the email will send to the address the user types in the email field. I'm not sure of the purpose of this however I still see knowhere to have the from address as the users email.
I have two drop down's (as attahced in the screenshot).
I'm running v2.3.2 (stable) with the latest revision of userforms 0.2.