BGR is covering the details of another RIM Blackberry Outage affecting about 80% of North America users. 

It looks like it's just come back up again but the outage started at 3am US time. 

In reading a lot of the reports it looks like it was BIS this time but another outage in less than a week since the last nationwide outage isn't going to be met with a great deal of sympathy from Blackberry users.

You can get more details from Boy Genius Report (credit to them for the picture above)