Most people who own a business will own a few for each domain; they'll mostly combine their email accounts using outlook express. They'll even use personal accounts at gmail, hot mail, yahoo, ect. and combine them with outlook, or login individually to each one. Some people have 2-3 email accounts, most full time work at home entrepreneurs will own 14 email accounts and up, the sky's the limit on the amount you can own and operate.
I have somewhere around 200. I've got about 100 sites and each one has an email address that forwards to my main address...then I setup throw-away emails in order to create multiple social bookmarking accounts. Got quite a few of those. Plus about 20 I have still up and running but mostly forgotten over the last 12 years.
I have no idea how many. I got one for each and every department in hosting, and then there's one per site. Then I have my personal two that I use for everything else.
around 5 one I use it for creating accounts and other stuffs so it will be full of spam usually lol..
I'm currently using around 5-10 right now.. How many do I actually have though?? The world may never know...