Usefull LJ feature

[snyders]

Ability to mark certain messages in the friend list as of special interest, and thus making them float. This would allow to watch long discussions that last several days or watch for comments in important topics. It can be realised by additional button, which will show all floating messages. The floating attribute may be set with expiration on time, or till the user unmarkes the message.

May be some clients already allow to do this. I'm using browser interface, so please enlighten me if this feature is already present.