It was a button in the profiles that told you if the user in question was online. It stopped working two, maybe three years ago.
They actually tried to fix it over a year ago, but this failed and created a lot of lag, so they disabled it again. =/
I'll get it working again.
Here comes another lamb to the slaughterhouse... sorry for my pessimistic view of the matter boppins, but there have been people before you that have tried and failed...
I'm not saying that I don't have any confidence in you, en contrare - I do!, but history has prooven me right so far...
*fingers crossed*
"I hope he's the real messiah..." ;)