I've received a mail from support with this answer:
thank you for your inquiry.
We are aware of the fact that you are not the only one having problems playing
multiplayer at the moment but we haven't received any information from
production on what to do or where these problems stem from.
Apparently there will be another patch for PS3, but no idea when it'll be
released or which issues it will address. But maybe these problems can also be
fixed by changing some of the server settings on our side, maybe it doesn't
need to be fixed through a patch.
Have you opened your public slots by the way?