PSN is currently having some problems at the moment, with the service having some trouble on PS4. PS3 and Vita users should be fine for now. According to the Ask PlayStation Twitter there seems to be a problem with users unable to sign in, though the cause of the problem is not yet known.
The PlayStation Network is currently: Intermittently available.
PS4 users may experience issues when connecting to PSN. We are working to resolve this issue as quickly as possible. Thank you for your patience.
This issue isn’t affecting everyone on PS4 though, so you may just be unlucky if you do hit by the problem. I’m currently signed in and quite a few people are online on my friend’s list. If you are affected then maybe give it a little time before trying again.
Update: Everything should be working fine now.
Source: PlayStation Support/Twitter
TheShepanator
Hopefully all of this downtime (aside from the DDoS attacks) is them using all the PS+ money to expand the network and make it more stable in the long run.
Carrot381
It’s been fine for me all evening.
monkeyspoon
I was having trouble with The Crew. But that may be ubisofts problem.
MrJimmy
I was kicked out of the PS store but Netflix was ok
cnutard
I haven’t been able to even infiltrate the store, on ps4, for over a week!
Andrewww
Had problems downloading PS Plus stuff on Thursday evening, but as long as I can play Alien Isolation, I’m happy… :o)