According to Community Team Leader Elixor's announcement on the French Official PlayStation Community (linked above), the Playstation Network has maintenance scheduled for tomorrow (Tuesday 14 October 2008).
It will be down from Tuesday October 14 at 21:00 to Wednesday October 15 at 02:00.
To quote: Hello all,
A maintenance PLAYSTATION Network is scheduled for tomorrow (Tuesday 14 October 2008).
Start: Tuesday October 14 at 21:00
End: Wednesday October 15 at 02:00
During this maintenance you can not connect to PLAYSTATION Network.
If you are connected before you should be able to play online without problem.
Thank you for your understanding. More PlayStation 3 News...