Update: It is now possible to say "bugmenot.com" on Facebook! I don't know if they noticed the story or if it was just a fluke, but hopefully they got enough complaints that they turned it off.
For a rather complicated reason, I was trying to mention a few URLs in my status message on Facebook. I got a strange message from Facebook:
Warning: This Message Contains Blocked ContentI looked at the message and figured maybe it didn't like three URLs in one message, so I tried the URLs one at a time. It turned out that one of them was the problem. I tried progressively shorter messages, until I discovered that you simply can't mention a certain URL anywhere on Facebook:
Some content in this message has been reported as abusive by Facebook users.

(all personal information is blanked out. click for full screenshot.)
The URL in question was http://www.bugmenot.com/, a website that lets you "find and share logins for websites that force you to register". There's no good reason for Facebook to be blocking their users from even discussing this site, as the word "bugmenot.com" is not abusive, and the site will not cause any harm to users. (In fact, it may protect them from spammy sites or sites that abuse their private information!)
It's more likely that Facebook is blocking BugMeNot from being discussed because, at some point, BugMeNot hosted logins for Facebook, and Facebook wants to get back at them by preventing peopel from talking about their site. Coincidentally, Facebook requires a login to view almost any content on their site.
While it's perfectly appropriate for Facebook to ask BugMeNot not to list logins from their site on BugMeNot (there's even a form for it), it's appalling for Facebook to block anyone from even mentioning the site -- it's plain and simple censorship, and it's unacceptable!