This Slate essay on the death of email is worth your time. Here's the main idea:
Those of us older than 25 can't imagine a life without e-mail. For the Facebook generation, it's hard to imagine a life of only e-mail, much less a life before it. I can still remember the proud moment in 1996 when I sent my first e-mail from the college computer lab. It felt like sending a postcard from the future. I was getting a glimpse of how the Internet would change everything - nothing could be faster and easier than e-mail. Ten years later, e-mail is looking obsolete. According to a 2005 Pew study, almost half of Web-using teenagers prefer to chat with friends via instant messaging rather than e-mail. Last year, comScore reported that teen e-mail use was down 8 percent, compared with a 6 percent increase in e-mailing for users of all ages. As mobile phones and sites like Twitter and Facebook have become more popular, those old Yahoo! and Hotmail accounts increasingly lie dormant.
I think this author is on to something, but I'm not sure the trend is as pronounced as it may seem. Anyone who works in a professional capacity still has an email account which they probably use throughout the day. And while Hotmail and Yahoo! accounts may lie dormant, Gmail accounts - which combine messaging, word processing, and traditional email functions - are spreading, at least according to anecdotal observation. One cause of the end of email - if email truly is ending - may be the rise of spam. As spam increases and efforts to thwart it fail, more direct and uncluttered forms of communication are likely to become more popular.