http://status.twitter.com/
It was, allegedly, a Denial of Service (DOS) attack that brought twitter to its knees.
Other useful accounts to follow:
@CalgaryCommute - Calgary traffic updates
@660NewsTraffic - ditto
@calgarypolice - their latest tweet was a link to photo radar locations for August
@CobraCommander - tipssssssss and trickssssssssssss for world domination