Hi guys! Sony has posted the following statement up on its blog regarding the PlayStation Network outage.

As you are no doubt aware, the current emergency outage is continuing this afternoon and all Sony Online Network services remain unavailable. Our support teams are investigating the cause of the problem, including the possibility of targeted behaviour by an outside party. If the reported Network problems are indeed caused by such acts, we would like to once again thank our customers who have borne the brunt of the attack through interrupted service.

Our engineers are continuing to work to restore and maintain the services, and we appreciate our customers’ continued support. For further information, please refer to updates on PlayStation.com, here on PlayStation.Blog and via our @PlayStationEU twitterfeed.
The Network has been down since late last night, and although Sony doesn’t know the exact cause, an outside attack should probably not be ruled out, especially with a busy weekend for the Network ahead.

Update
Via EU PS Blog

While we are investigating the cause of the Network outage, we wanted to alert you that it may be a full day or two before we’re able to get the service completely back up and running. Thank you very much for your patience while we work to resolve this matter. Please stay tuned to this space for more details, and we’ll update you again as soon as we can.

Source Find on: FiveStarGamerz.com

My first thought would have been Anonymous, but they promised to stop DDoS'ing the PSN after people complained. Could be some other group though.

Also, article here
It looks as though either a different group is attacking PSN, or Sony's had a SNAFU.

Its annoying as hell is what it is.

I figured id be able to play some Black Ops or some DA2, but without being able to get into PSN, its no fun doing either.

Source:

FiveStarGamerz.com
Letter send to Sony by anonymous Hackers

Hackers promise revenge on Sony for abusing the judicial system in an attempt to censor information on how products work. This shows that sony's problems are just beginning for safe guarding the PS3. As most of us expected the war between Hackers and the console manufacturer's is just getting started. Below you can see the latest post to sony regarding this subject. Please share your thoughts on the subject in the comments section below. Do you feel sony should lay off on the relentless pursuit of Geo Hotz or do you feel they are doing what's best for all of Sony and the future of console gamers? One thing is for sure, There will be more to come following this.

Uh oh... Anonymous?
Update: At least you can still get on Netflix, despite PSN being down; I as well can confirm this working:
Update: I guess Sony is just having one of those days -- Anonymous is not at fault for the downtime. From their IRC channel:

We Are NOT attacking sony, psn or any sony sites
Asking if we are will result in a ban from our irc
Psn is down because of sony NOT because of anon
Our DDoS attacks on sony have stopped
So fuck off asking

Dude... that's old news.
Geohot (George Hotz) has settled with Sony (having been served with a permanent injunction), and Anonymous has, on their irc stated that they're not responsible for this. That was mentioned in the article I posted above.

The letter above was sent by Anonymous before they started DDoS'ing the PSN, an action which they have since ceased because of complaints from PSN users. The video that accompanied that letter has since been removed from Youtube for "violating our [their] terms of service".

Operation Sony since then hasn't gone so well since Sony had security called in and their stores closed on that particular saturday (a protest was encouraged on the 16th of April) in an effort to prevent the protests. Sony still lost out on sales (however marginal) on that saturday, so not a complete loss.

ALSO this thread seems like an advertisement for this "FiveStarGamerz" website.

Is not an advertisement, I posted the Website because I didn't wrote it,
and im just adding the source of this article.

Anonumys Sucks he hacked ps3 i cant connect to anything luckly sony Is in Maitanence

1) Anonymous is "they".
2) They didn't hack the PSN this time.

Sony cause this problem and they wont admit it.
Beside, the hackers "anonymous" said: "they
will hack Sony not the people of ps3."

Latest update:
Wat you know they lie about
saying the problem was in japan and now they say
there was an intrusion....? Come one tell us the truth.

Latest update:

An external intrusion on our system has affected our PlayStation Network and Qriocity services. In order to conduct a thorough investigation and to verify the smooth and secure operation of our network services going forward, we turned off PlayStation Network & Qriocity services on the evening of Wednesday, April 20th. Providing quality entertainment services to our customers and partners is our utmost priority. We are doing all we can to resolve this situation quickly, and we once again thank you for your patience. We will continue to update you promptly as we have additional information to share.