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.