It just dawned on me today that I've noticed a recent trend with Lync.
While I start conversations with IM, they almost immediately become an audio call.
There are a few folks that simply do not like typing which makes sense but ultimately the result is far better as you get more of the persons speaking tone, and the conversation can move dynamically as the topic continues.
Another aspect of audio is that you are speaking with that person and they become more human to you as a result, not just some faceless entity you are working with.
Video I still don't see the uptick on, for myself it is because as a remote user working from home adding video many times causes the quality of my audio to drop.
To a lesser degree I am also picking up on those people who don't require the cordial IM asking if they are available. This tends to be those on my team or that I work with on a weekly basis, and most also work from home or have been with this technology for considerable time.