Let's say you don't want people to have to enter a password to login, then you can create a custom landing page, form and newsletter notification to send your customers a magic link to login.  To set this up, follow these steps:

1. Setup a new form that simply asks for their e-mail address, make sure that you map the field to the e-mail address attribute.  And the form should be Multiple Responses enabled.
   
   
   
2. Then create a new landing page and assign the form you just created.  Make sure to add the
   tag to have it pop up on your page.
   
   
3. Now setup a new E-mail Notification that is assigned to the completion of that form.
   
   

When they complete the form, they will get an e-mail to auto-login to their account (or wherever you send them).