How does Facebook decide which friends show up in your chat list?

[TC]

On Facebook you have the bar on the right hand side with all the friends you can chat with... the top section is a mixture of online and offline friends who you speak to most regularly.

Does anyone have any information on how Facebook decides which friends appear in this list? How much you have to speak to them, what period it tracks information over etc? If you didn't speak to someone for 6-8 weeks would they still be in the list?

[billybob]

on how often you speak to them and how big your convo is, and still going, doesnt depend on how long

[Christie Hemme]

I think Facebook chooses those friends you recently/regularly interacted with on top of your chat bar. Interactions is not limited to chatting or talking to them, if you keep on "liking" their statuses/pictures etc or commenting on their wall, those will appear to Facebook as interaction with that particular friend.