I've got one friend who only wants to communicate wall-to-wall on Facebook, one that prefers Skype, several who'd rather instant message (of course, none of them use the same client), some use email as if it were a chat client, and some just won't respond to anything but a phone call, although they never respond to voicemail.
So what's the deal? Who prefers what mode and why? I imagine most of use a combination of modalities, but clearly for day-to-day, run of the mill communication, people have preferences.
(n.b., it was Michael Sperger's article in the July/August CIM that got me thinking about this)