UPDATE 4: Around 3:30 PM ET on August 11, full service returned for nearly all users, according to service status reports on DownRightNow.
UPDATE 3: Problems persisted at 10:30 AM ET. According to TechCrunch, the issues may be due in part of the site's experimental features, which are currently being tested among small groups of users, who have reported various tweaks to the Facebook Chat sidebar. Read more about these experiments here.
UPDATE 2: Facebook's issues were largely resolved in the morning on August 11. At 7 AM ET, however, DownRightNow showed intermittent issues on the site, and some on Twitter said they were still unable to log in.
UPDATE 1: At 11:30 PM, a post on Facebook's Known Issues wall read, "We're currently experiencing an issue where some users may experience some slowness or timeouts while using the site. This issue should be resolved shortly."
PREVIOUSLY: Many users took to Twitter on Wednesday night to report problems accessing Facebook.
According to DownRightNow, the social network began experiencing problems sometime before 10 PM ET.
Around 11 PM, DownForEveryoneOrJustMe reported that Facebook.com was still up, though login attempts were not successful at that time.
Facebook's official Twitter feed has not addressed the problem.