Do you know that Gtalk can be used as an answering machine? Yes, it is possible. So, whenever you are away or busy with some work, you can instruct Google chat to send automatic replies to friends messages.
GtalkAutoReply is very useful application to notify your friends about your absence from your desk. Alternatively, you can hide your current status and force it to idle to trick your friends. In this application, you need to provide your Google login ID and password and then set the automatic reply message. [Download here]
Friendly advice: Your auto-reply message must contain some text indicating that this is an automatic reply or else the receiver can be confused.