Between Twitter and email, the @ symbol is probably the character I type the most (unless we're including punctuation marks, because I am a very bad overuser of the exclamation point). I've always loved its swirlyness, even in the pre-Internet days when I wasn't really sure what it ever got used for.
In grad school, I came across it in medieval manuscripts I was transcribing for a class, which was kind of neat. (Transcription is hard work; I totally get why those scribes wanted a little shortcut!)
The current issue of Smithsonian has a nice little history of the @ symbol. Did you know the Dutch call it the "monkey tail"? I think I'm going to start using that.
If you are a punctuation/typography nerd like me, you can read the full article here: The Accidental History of the @ Symbol
PS: SciFi fans, Smithsonian.com also has a neat article about ten inventions inspired by Science Fiction, including the cell phone.