We'd hardly call it a ground-breaking feature, but it's pretty nice that Facebook now lets you know whether the friends you're chatting with are using the mobile app or the website. To the right of a user's name you'll now see the words "web" or "mobile," letting you know whether or not a buddy is seated in front of their PC and ready to chat, or out and about firing off rather brief replies. People started noticing the new feature pop up
