It seems that WA is still working on this one. I would like to throw my vote in to please change the login method. Like previous posts, my organization has a little more than 6000 members at the moment. Of these members, we had to set 2000 of them to dummy emails because of families that use the same email address for multiple members.
Most sites don't require the email address to be the login. Most just require a username of some sort, you can enter your email address as the uid if you want. The problem also arises that people change their email address, when they get sick of aol, yahoo, hotmail and want to switch to gmail or something. Or what if a person signed up with a cable company, and that company gets bought out, or they decide to switch providers? Then the uid has to get changed.
I say, username should be just that, username. Easiest work around might be to default it to email address, since most have it, but have the back up be alphanumeric.