I added the following code to allow a registered user to login on the checkout page (ecommerce/templates/Layout/CheckOutPage.ss) so all their information is recalled from the database.
Sam Oltz
Spearia, Inc.
<% if CurrentMember %>
<% else %>
<div class="typography">
<h3>Login</h3>
<p>Already have an account? Login here.</p>
</div>
$LoginForm
<% end_if %>