If someone places an order who is a member, but not logged in, you receive the following alert messages:
Sorry but form validation has failed, please check for errors
Warning: E-Mail Address is already registered!
If you then login you are redirected away from the checkout page to the "My Account" page and the customer has to navigate back to checkout. Would it be possible to stop on the checkout page once you login or have a radio button option to checkout as a guest instead of logging in. I think if someone logs in from any page they should stay on the page they logged in at. If they want to visit the members area they have the option to do this with the drop down menu top right.
If customers are taken away from the shopping cart it may end up with a lot more abandoned carts.