When autofill occurs, its not so clear, I mean, if you type several addresses, you have to separate them by commas, etc... In some webmails, when you type an address and hit enter, it clearly gets "entered" into the system. and appears in a diferentiated way, then you can easily add 1 more address, without having to use a separator, etc. Friendlier.
Also, pls consider autofill of emails that one types but are not in their contacts (even if optional).