Unibox works pretty well for newsletters and notifications. They get grouped into one contact by sender, so e.g. 4 Twitter notifications only take one slot in the contact list.

It works also really well for notifications that contain attachments. If you have e.g. a github account that sends invoices you can select the Github Billing contact, go to the attachment list and have all invoices in one place. I don't copy attachments to the filesystem anymore because it's much easier to find them in Unibox.

What do you for business? My use for email is communicating with clients (all real people :).

if I look at my raw mailstream his case might be correct, I aggressively use filtering so most of what makes it to my inbox is actually mail.