It's very nice. The only suggestion I have is to either make the thread starter match the PM sender or have a seperate option to choose a thread starter username. Currently threads are started by the trigger account.
A nice bonus would be to be able to exempt usernames (ie, so admins don't trigger the function logging into a test account and such).
Still, VERY handy feature and I see no problems as of now (barring the ae_multiplelogins_thread template being uncached).