During implementation, we´ve decided against it as it´s really easy to clickly click away messages without reading them. Of course these messages could become annoying if they are running for days and you see them multiple times a day.
Our assumption for this feature is that it´s primary use case is to inform about upcoming events or recent changes - so messages should only stay up for a short while.
Is your use case different or are your users logging in many times a day?
