Kazua Hiraj has announced that Sony has begun a region by region activation of the PSN today. It is suggested that after you turn on your PS3 and update your firmware you immediately change your password for the PSN (like they have to tell you that). They are slowly getting to each city and state and are saying it will be "several hours to restore PSN throughout the entire country". As of this writing at 8:53 PM MST only 7 Northeast states had their service restored and given their estimate, we should be seeing a nation wide return to coverage by Sunday morning. This is assuming they work on it all night. If you would like to see the status on the return coverage check on the source link. Good news is now you can start get Portal 2 on your PC for those that have it on PS3 and Mortal Kombat can start to see the online play it deserves.
EDIT: We now have a full return of the PSN.