For someone who moves words, numbers and other various information concepts across the globe on a daily basis, email just doesn't cut it.
It's great for someone who receives and sends e-mail analogous to postal mail, but when you've got hundreds of messages coming in every day any professional 'data manager' will agree we've got a long way to go.
We're not talking spam here either, but actual information I want to receive, but have no other interface to exchange it with other parties outside of e-mail. It gets even worse when we look at the amount of attachments we process on a daily basis. (assorted musings on this from Adam Curry)