The Central Desktop Blog tells us all the reasons why e-mail is bad and explains why you might want to seek out a better solution for your collaboration.
The single worst trait of email is that it's silo'ed. What I mean by silo'ed is that email traps information into personalized, unsharable, unsearchable vacuums where no one else can access it – the Email Inbox. Think of your Email Inbox as a heavily fortified walled garden. Not mentioning the difficulties many have accessing their Email Inbox outside the corporate firewall, the Email Inbox contains a hodgepodge of business, personal and private information that most people do not want to share with others.
E-mail probably isn't going anywhere for awhile and despite it's problems can still be a very useful collaborative tool. However, as the article states, there are many other tools popping up all over that could very well suit your collaborative needs better. The Bad In Email (or Why We Need Collaboration Software) [Lifehacker]