Actually, I'd prefer that coworkers don't start blowing up my phone/PC with chat alert beeps for an extended question until they've confirmed that I'm not in a meeting/trying to concentrate/etc.
Also, there are people change the status to 'busy' when they are not actually available, extended lunches and what-not. And there are more people who forget to reset their status to 'available'. So setting status to 'busy' is no guarantee that you will not get a ping. Or a phone-call.
I have seen the embarrassment on people's faces when in a meeting and their IM app starts beeping like a time-bomb after someone has cut the wrong-wire.
The sender sending a short 1 liner and waiting for acknowledgement before proceeding would prevent this. (results in a single beep if the receiver is busy)
Its also avoided if the sender simply sends their entire query as a single message. (again results in a single beep if the receiver is busy and doesn't reply)
I've started using the "Do not disturb" option in my Office Communicator when am in important meetings. Using that option on the communicator makes it impossible for someone to send me a message. Any attempts explicitly fail on the sender's end with an error stating the obvious - The receiver has set "Do not Disturb"