On the PlayStation forums, a Sony community manager gave us the heads up that PSN will down for maintenance on Thursday, November 7 from 8:00 AM to 3:00 PM Pacific Time.
"If you've signed onto PSN over the past few days, you'll still be able to play online and access apps during this period, but you may receive a maintenance notification when attempting to access the PlayStation Store, PlayStation Home, and Account Management as these services will be unavailable. Be sure to sign in now if you wish to access the Network during this maintenance window.
Thanks for your patience during this maintenance timeframe, and we apologize for any inconvenience this may cause."
So to clarify, online will still be active and available for those who have been logging in regularly. However, if you have not logged recently you might not be able to play online for the duration of the maintenance period. If you don't want to be offline during this time, be sure to turn on your PS3 and log in.