Finally, at last, this office has in-house IM. Thanks Notes Sametime. We also have email, can walk around to speak to people (assuming that they are anywhere near you.. lots of people are in other states..) and can phone... or fax.. or if desperate send a letter or Memo[tm] (long story, don't ask).
IM does not replace email. IM is 'instant on' the person needs to actually be online to have a synchronous 'conversation'. Generally, you only have a conversation with one person at a time. Rarely, two or three people.
Many times I need to type up information, wrap it up with colours and hyperlinks and send it to 5, 10 or 50 people. Email does this. Nothing else matches it.
Maybe I could do the same in a .doc and then... email.. or IM.. the doc?
Perhaps I could create a wiki page and then.. email? IM? the page to everyone? but how would everyone know who to reply to? Hmm.
While I can agree with the statement in the OP that only a small percentage of emails are directly relevant to 'business' .. it's also true to it is a primary communication channel for customers and currently has the best software install base.
The only way to reduce email I have found is to install Service Desk software - which reduces problem, incident, request and change emails.. and consolidates them into one place. Reduces. Does not stop. When you need to communicate, then regardless of your help desk solution, it still comes back to email, phone, IM, fax or posted letter (and probably in that order).
Now, I have to get back to this email that I've been drafting all day which should have been sent yesterday..