I believe in the outage thread someone mentioned that they thought an upgrade caused the outage... turns out that's the story RIM is going with:
R.I.M. Offers a Reason for BlackBerry Failure
Beginning of article:
OTTAWA, April 19 — The installation of an insufficiently tested piece of software set off a chain reaction that eventually cut off BlackBerry service to more than five million users in North America users, the devices’ maker said late Thursday.