Here's some information from Engine Yard (our hosting service provider) about yesterday afternoon's data center outage, which affected a number of applications including Pivotal Tracker:
http://blog.engineyard.com/2009/03/31/march-30th-outage
We apologize for the inconvenience this outage caused, and appreciate everyone's patience. As detailed in Engine Yard's post, steps are being taken to ensure that this does not happen again.