If you are running a lot of tests between diffrent roles and workflows, in diffrent browsers, diffrent users, but don wanna read diffrent mailboxes and accounts, this is a way to go.
I also use in buddypress installs with fake members during releases / campaigns and communicate with diffrent users with my diffrent fake members. All mail notices are running into ONE mailbox, and I can access all my dialogs through one address.
Superb tool in projects.
I use Latest WordPress 3.5.1 and the plugin Allow Multiple Accounts works fine. I also have an install with Buddypress 1.7 and it works great on that combination too.
All email notifications are alright.
My single WP install also uses a login plugin, and the ajax calls are also ok with this oldie.
UPDATE: As of 2015 we still use this plugin all around in diffrent projects. We are happy that the author of this plugin did an update for more later versions of WordPress like 4.x.
It works fine with Woocommerce to!