People that are online, doesn't always show up, messages are lost, notifications doesn't come in for everyone and are unreliable.
This happens quite often since the new messaging system was established, followed by the new chat bar, that makes it apparently worse. I'm very frustrated. People want a response, but messages don't show up at all time. Suddenly I get a message from someone in the chat window, but Facebook indicates no one is online. Keep an eye on that. What is shown left is not true. And yes, the side chatbar is off. Inside the bar, it's the same problem. This has been going on for many weeks now. I also got no response from the Facebook-Team.
If Facebook goes on like this, it's completely unusable for important messages. And all my messages from friends are very important. Even more important than some business stuff. It's about my friends, you know...