Last Updated Jan 9, 2011 11:49 PM EST
First, a refresher for those of you who might be unaware: When you enter an addressee in the BCC field of an e-mail, that person gets the message, but everyone in the To and CC lines is unaware. Hence, the "blind" in BCC.
These days, I'm seeing people use the BCC as a way to hide recipients behind a curtain so those folks can see messages it's perhaps not entirely polite or ethical to share with them. An extreme example: BCC'ing other people on a disciplinary e-mail that you're sending to one of your employees. Or BCCing a potential vendor on an e-mail in which you're discussing their bid with your finance guy.
In either of those woefully misguided cases, you might have the best of intentions, but imagine what happens if one of the cloaked folks on the BCC line clicks Reply All, either intentionally or by accident. The cloaking device gets turned off, and everyone can see you had included secret recipients in the original e-mail. Trust me: You don't want to be standing in that particular poop storm.
Photo courtesy Flickr user lara604