Ok.. If you found my blog, you were probably thinking that it was not possible at first but it is.. It's possible to be invisible to only a specific number of people, poeple who are strangers who you just add up on fb without wanted to communicate with or if you just want to be online to your boyfriend or girlfriend, it can be done..just follow the simple steps..

1) Go to "account"
2) Go to "Edit friends"
3) Make a group for your:

(example)
-for my boyfriend only
-strangers
-chat with

etc.

4) Select the specific people you want to enter or put in that group. You do that by going to "edit list" beside their names in your friends list and checking what group you want them to join.

Read more here..http://marianjanealumbro.blogspot.com/2010/10/how-to-be-invisible-in-facebook-chat.html