This is reason enough to stop using Facebook mail and/or to cancel your Facebook account. From the Wall Street Journal Digits blog:
"Last night, in an embarrassing glitch for Facebook that raises questions about privacy on the site, some users of the social-networking service began getting hundreds of personal messages that weren’t intended for them. A WSJ.com editor, Zach Seward, tipped Digits off to the apparent glitch after his Facebook inbox was flooded with messages ranging from the mundane to the truly private... Mr. Seward, who received emails from about 100 people, said the deluge started at about 8:30 p.m. and that he was later temporarily unable to access his Facebook account. Facebook removed all but two of the messages. But like many Facebook users, Mr. Seward has these messages sent to his third-party email account, where they remain. He said he has not heard from Facebook regarding the glitch... It is unclear how many Facebook users have been affected by the problem, but several Twitter users reported the glitch."