Starting tomorrow at 2 PM EST, the PSN will be down for what is being called "essential maintenence".  It looks like Sony has a bit of server work to do as they also announed that the PlayStation 3 2.5 firmware is coming tomorrow.  What new features will you be getting with the new firmware?

• Pads and the PS3 itself now have tweakable power-save settings for turning off after a period of inactivity.
• You can tell the PS3 to power down once it's finished downloading or installing content.
• In-game screenshots can be taken in compatible games.
• It enables high-quality mode for the official PS3 Bluetooth headset.
• The Trophy interface has been improved, so you can see you and your friends' progress more easily.
• Friends now have their last login time listed.
• Videos now have a scene search feature.
• There's a button on the PlayStation Store frontpage for redeeming codes.

The other speculation here, and some that is probably spot on, is that this downtime is prepping for Home.  Considering Microsoft just did the same thing to prepare for next month's NXE, I'd say that is a great guess.