It has recently been announced that Sony will be carrying out some emergency maintenance on the PlayStation Network today, details are scarce however a post on the EU PlayStation Blog suggests that the work will start at 16.00PM and end at 19.00PM.
Early on during the maintenance time it is thought that PlayStation Network users will not be able to use PC registration, also if try to access the PlayStation Store, Registration or Account Management between 16.00PM and 17.30PM you will probably see a maintenance message.
The good news is that the maintenance will not affect online gaming, therefore you will still be able to sign in to the network and play online game modes without an issue.
It is unclear what this emergency maintenance will entail, however we have not heard any rumors regarding new features or optimizations, therefore we expect no major changes once it has been completed, when we find out more we will keep you posted, for more info check out this link.
We would love to hear from you if you have experienced any PlayStation Network problems during the scheduled maintenance, be patient if there are any weird problems as things should be back to normal within a couple of hours.
Also See: PS4 update 2.0 specifics for SharePlay