Change the MTU numbers in the Network settings, it doesn't matter what numbers you pick and don't change anything else, and when you are done, the MTU numbers will reset, and the entire PSN session will reset as well and everything should be working. atleast it did for me and couple of friends, and it worked for the person who brought it up in a thread. It's worth checking out. better then to just wait.

Does it work with an MTU of 1976?

Sometimes.

It did for me, it's worth checking out if you haven't been granted access to the PSN

Sorry I'm just joking. 1975 MTU size is a completely arbitrary number. It absolutely doesn't matter if you set it on 1501 or 9000. It is not what is fixing the connection anyway. If it actually works and is not just coincidence the reason will probably be that the console will have to negotiate completely new sessions which the PSN accepts when it has free capacities.

I assume if that fixed your problem it will also still work if you switch the MTU back to normal.

It automatically goes back to 1500. it's a lot better then reseting your router and all. it's worth a shot for those who still can't get in. if it's resets the session it's still good. cause people walk around clueless and don't know what is going on or what to do. i am sure it was no coincident, cause i told my friend, and they got automatic access after they tried. well i guess it doesn't matter which number, but i tested that number. i am just trying to spread the word. 

More power to you then.