See this snapshot:
Which friends' come under the "More Online Friends" List?
Okay, now many of my friends are offline; why is it that some of them appear in the main list (as offline) while others do not.
I see many friends I never interact with on my Main List and a few I recently chatted with on facebook in my "More Online Friends" List.
What's the algorithm behind this sorting and categorization?
Best Answer
I believe that the "Main" section are friends you have put into a specific list. The "More Online Friends" are friends who are not placed into lists.
The lag in online/offline inaccuracy is due to the refresh rate set by Facebook.
Facebook is HUGE. They have a refresh/cache for the online/offline of users. Different areas most likely have different cache/refresh times.