As you might have noticed, I’ve moved this blog to mw2tactics.net. I hope to see you there!
There’s apparently a problem with PSN, which makes signing in impossible (and therefore MW2 multiplayer also). Some say it’s like a millennium-bug and that your Playstation thinks that it’s 02-29 instead of 03-01. Sony is aware. It seems only the older models are affected and the Slim ones are fine. To be clear: Sony made a statement that you should not use your PS3 until this is fixed (or if you have a Slim model).
For more info: Playstation on Twitter, Playstation blog
The problem seems to be fixed. You can safely use your Playstation, although you might have to adjust the time manually. For more information you can look at this entry on the Playstation blog.