See part 1 for the background of this webcast or part 3 for my impressions after cutover.  Cnet also has an article on the last minute delays.
Interesting tidbits from the live webcast.  I’ll be updating this post as I watch.
8:55 CST:

They commented about all the traffic they are getting now through the backdoor they left [...]

The process of bringing Wolfram Alpha online is being webcast live right now.  It starts with a 5 minute intro along with some other pre-recorded clips.  Some interesting tidbits:

it will be run on thousands of CPUs
it is planned to be a 48 process – presumably shooting for being fully live Monday morning
the webcast will include [...]