I think everyone I know has well over 100 emails in their inbox. I've seen people with over 1,500 emails there.
Mine has zero. It rarely has more than 6.
One Saturday night about 18 months ago my daughter was at a Bar Mitzvah party. We were hanging out at a nearby Barnes & Noble passing time until the party was over. About 11:00 pm that night I wandered into the Microsoft Office section and saw a book called Total Workday Control Using Microsoft Outlook by Michael Linenberger. As my typical workday never seems to be in control I took it off the shelf, looked at it and then bought it. I bought the second edition when it came out during 2008.
Linenberger makes a very good point early in the book about the purpose of the Inbox. He uses a story about how people, in the days before computers, used to have 3 stacked trays on their desk. The top one was usually for receiving items - the Inbox. Once you looked at something there it never went back to the Inbox. You either put it in the Outbox, filed it or put it in an in process tray. Microsoft deliberately named it the Inbox - the intent was never to keep 1,000 emails there. You would read something, act on it, and keep it out of the Inbox.
Most people keep emails in their Inbox so as to not lose track of tasks that have come in with those emails. Others don't have an effective filing system. For some it is both.
At the time I first read the book, I only had about 30 emails in my Inbox. Using the tools Linenberger provides, it now is generally empty. Read it, decide what to do with it, then file or delete it. Simple.
The strength of the system is properly configuring the Tasks module of Outlook. I don't think many people use the Tasks module, but after making some common sense changes it becomes quite powerful. All you do is drag the email from the Inbox to the Tasks button in Outlook and boom it becomes a Task with the text of the original email intact. You can also create Tasks with any attachments - nifty.
Linenberger is an advocate of topic based email filing. I have always created specific folders for filing email, but I see the beauty of this part of his system and am preparing to implement it. All email will be in one folder.
I am not saying my workday is always in control. But using Linenberger's ideas, I am not losing track of nearly as many things I need to do, and my Inbox is usually empty.