True, but I also need people I want to talk to to be on the messaging tool, which is the real issue here.

As for email, to me it just doesn't serve the same purpose that IM does. It's analogous to sending letters back and forth as opposed to having a face-to-face conversation -- the increased time lag between replies encouraged by the medium has a huge influence on the nature of conversations that occur through it.

I still use email, for example when I want to send something more in-depth to someone and I don't expect a quick reply. But it's not the right tool if I want a real-time, informal conversation with someone, which is most of my conversations.