I've always thought @ meant at, not about.
Yes, it's a new Twitter thing. Every member name has the @ before their member name. People are inappropriately putting it in non Twitter places and onto screennames OFF Twitter. Not everyone is @(screenname) when it isn't even about Twitter.
Like here, instead of responding to the OP by quoting her or simply calling her by name, some people would say:
"@DisGirlAllie, the use of that symbol means. . ."
But THIS place isn't Twitter, it's the DIS. And the other places you've seen it used aren't Twitter, but they will use the @.
Now I get it! I had no idea why my niece (freshman in college) had taken to calling everyone "@Name" on Facebook. 
I think of myself as fairly internet-savvy, but I don't twitter. Not yet, anyway. 
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Thank you for explaining this!
I've read this whole thread, and I still don't understand what you all are saying @ and # are being used to mean. I am not reading "at" or "about" with the any examples of the @.
What is it you are saying # means besides pound or number or tic-tac-toe?
As a symbol, I've never heard of @ meaning anything but "at". I guess it has some official name, but isn't it known as the "at symbol" in typing class?
On Facebook I have seen people type things like @KristaTX and it still confuses me. I finally figured out that it means a comment is directed at KristaTX, but when I type a comment directed at a specific individual, I just type "KristaTX - blah blah blah" like I would in a note to someone
Plus Twitter is Twitter and Facebook is Facebook.
.Yep, perfect example.
The problem with that is you aren't on Twitter yet. When you go to join Twitter, there may already be an @Laurie31, or you may decide on a totally new name, like @Laurie3100 or DisGirlAllie may want to be called @TwitterGirlAllie. So when your niece is improperly using it, she might be accidentally using someone else's Twitter name or referring to you by a name that you don't/won't have.
I don't know a lot about Twitter, but as far as I know, an appropriate use of the @(screenname) on another site or correspondence is when quoting someone from Twitter. Like when we post a news or web article, we include the corresponding link. To refer to a Twitter Tweet, one would say, "@(screenname) just Tweeted this joke or picture. . ." Then people would know to go to Twitter and enter @(screenname) to find that person's corresponding Twitter page. The @(screenname) IS the link to their Twitter page.
Your niece is referring to you as @Laurie31, when you don't even have a page.
People are inappropriately putting it in front of people's names on FACEBOOK - not Twitter, when some people don't even have a Twitter page.
If people went to the link for @KristaTX <- - that is what they would get, because you don't have a page, but your friend is referring to you like you have a Twitter page.
