Twitter, IM, Social Networks, haven't replaced email, and while Google Wave does seem quite cool, I do not see it replacing email any time soon. From what I've read, it's pretty complex, and Google may actually have a rough time generating a positive network effect in the near term. I could see wave being great for some conversations [group event discussions, planning, etc.], but not sure it will be appropriate for transactional and business communications. Wave certainly seems like a disruptive technology, and I am quite psyched to check it out and learn more, but I believe the future of email is bright. Those of us concentrating on delivery probably still need to worry much more about the Gmail inbox than Wave.