As long as players have signed in to PSN five days prior Sony said you may still be able to play games online, as well as use Netflix, HULU Plus, and Music Unlimited.
PSN maintenance is going to take more time then expected, and according to a tweet by PlayStation will hopefully be complete by tonight.
ORIGINAL: PlayStation orginally posted on their blog that called for maintenance for Thursday between 11 a.m. To 11 p.m. ET that would affect the PlayStation Store and Account Management. However, users were and are still able to access online play and apps as long as users signed into PlayStation Network at some point before the maintence took place.
The purpose of the maintenance was neccesary Sony said so the company could continue to put online games on PSN. Playstation hasn't said yet exactly when the maintenance will be done, but Playstation users will have to wait a little longer.