Mentions are invention of Twitter rather than Facebook, like Facebook Hashtags who arrived later, although in Facebook were similar with photo labels, but not the same, and in each network there with subtle differences that are interesting to know, so let it.
A mention on Twitter or Facebook is only when we talk about someone and we want that person to know, do mention to be is notified of that has been mentioned, it seems a bit trackback blogs and what we talked on Monday, the references to a tweet that Twitter show, but between people, rather than between articles and tweets.
A mention may also be made silent, and talk about someone without such person or entity finds out, in fact, make it easier silent, that to make it normal, because the explicit mention do require a little extra action and therefore a manifest intention.
MENTIONS ON TWITTER
On Twitter, to mention someone in a tweet, simply type the @ symbol followed by the user name (url) to mention, not using visible name. That is, if a friend is called Jonh Smith and his username is jsmith, write @jsmith in the tweet to mention.
In fact, when we put the at sign and started writing @jl .. Twitter will suggest contacts that match these two initial letters in your user name, even if they do not we follow him, nor do he follow us. We therefore mention to any user, though not connected with us.
When you mention someone on Twitter, writing correctly their username, this person will receive a notice in its section Connect, so if he wants can reply.
MENTIONS ON FACEBOOK
In Facebook is something different, when we want to mention someone. There are two variants, if we do it from a personal profile or fan page. From the personal profile, writing also put the at sign or without, I can mention any fan page is not a fan though, but I can not mention to anyone, I can only mention people who I have as friends, ie invited and accepted my invitation. And unlike Twitter always be visible using his real name instead of your user name (the url of your custom).
If for against, we use Facebook as profile fan page, we will not be able mention nor to our friends, although we have on our personal profile as friends. In a mention of Facebook pages we can only mention the fans of the page, those who gave him Like. Thus, it greatly limits the mentions on Facebook, only to that particular circle of followers, and as with personal profilesand can not to mention who in theory is not known, or who has not been connected.
When mention someone in Facebook writing his name correctly, this person will be notified in Notifications, so if he wants can reply.
As you can see they are very similar but hide their little quirks. Although I do not know which is closer to reality or more just. Have I left a difference? Which of the two ways you like more or you think is more accurate and why?