hello all

is there a way to use the email address as the login username?

Oh boy do you!  I needed to do a variety of things to get this to work.  I REALLY REALLY hope that DNN adds support for this in the future.  It was a pain in the neck.  You need to do 3 things (in this order).

1. Create a custom Membership, Profile and Membership Data provider.  In the Membership Provider, you need to rewrite a few methods to switch the username with the password.  The other providers are needed just for everything to build properly.
2. You comment out the code in the ~/admin/Users/UserSettings.ascx.vb file that alters the Display Name using the Token (in the cmdUpdate_Click method).
3. Then change the User Token to be something that DNN doesn't use.  For instance [UNKNOWN].
4. Change the localization for all references to the term "User Name" to be "E-Mail Address".

Steps 2 and 3 allowed me to reassign the desired username to the display name in the custom provider, while at the same time disabling the ability for the user to change it.  This will keep the Display Name unique since it is passed in the code as the username still. 

Step 4 will prevent possible confusion from the end-user who may try entering the Username instead of the e-mail address.