A lot of people have it turned off. I turned mine off a long time ago. I have no intention of being put on the spot by someone I have no interest in. The other thing that bugged me was that you could be chatting with someone and other chat boxes popped up. The chat also doesn't work right for some people. Best bet is to just send a regular message.
Considering the rate of response from messages sent is less than 1%, I would take any option I could get.