UPDATED:  Contest Closed, We Have a Winner!

P Kumar has won in impressive fashion.

No one has sent in a correct answer yet.  Two things I think are worth pointing out:

1) The logins are visible in the UI, and don’t require you to go digging through obscure files on the hard drive to find

2) They appear in PowerPivot for SharePoint, NOT in PowerPivot for Excel

Happy hunting.