Update: 1:40pm EST - ZDNet has official yet vague word from Facebook:
Earlier this morning, we encountered issues within our network that resulted in a short period of degraded site experience for some visitors. No user data was at risk and the matter is now resolved for the majority of users. We're monitoring the situation to ensure that users continue to have the fast and reliable experience they've come to expect from Facebook... We are investigating potential foul play at this time.
Update: 12:53pm EST - Fox Business is reporting that Facebook has confirmed attacks on its site. No official statement published on FB blog or press release yet.
Many people and bloggers have noticed that Facebook has been slow today. Live Journal was also down. This was all happening around the same time Twitter went down due to Denial of Service attacks.
There's no concrete reason yet, but one guess is increased traffic to those sites due to Twitter being down. Another possibility is an attack on those sites as well, but that is just speculation at this point.
Keep staying tuned.
What are you experiencing? Share your experiences in the comments.