Sony sent out a tweet notifying users that PSN servers are experiencing technical issues. "We're aware that users are experiencing issues logging into PSN. Thanks for your patience as we investigate," per Sony's tweet.
Services affected include account management, PlayStation Now, PlayStation Vue, and various social and gaming functions, including the ability to log in and play some games. The PlayStation Store is still up and running, so PS Plus subscribers can still grab the batch of free games that went live for PS3, PS4, and Vita earlier today.
You can follow along with Sony services on the status page, where Sony posts updates.