I have my own domain for personal email, so I theoretically have an infinite number, as I can choose anything I like before the @ sign. All those different addresses are redirected to my gmail account, so they are all in one place. This is really useful, as when I sign up to a website, I put in something identifiying the website in the bit before the @, and if I start getting spam at that address, I a) know who sold my address and b) can easily block that specific address. It's also easy to filter emails this way too. Lastly the best thing is that gmail can be set up to send mail from any address you can prove you own. This means I can reply to someone that emails me on a specific address from that address, without my gmail address appearing.
1+2+3+4+5+6+7+8+ ....... +(N+1) number of email accounts . In that 1+2+3+4+5+6+7+8+ ....... +(N) accounts in gmail
It's really annoying how everything these days needs registration and user/pass/email, and for different reasons you don't want to use same info for everything which forces to get dozens of email accounts too, can't remember how many but it's a miracle that i remember most of them and all different passwords.