The first thing you ask a child who is not connected a internet, Whats the use of Internet is? He will reply to send emails. Infact the main reson behind Internet Being such an Hit is email only.
Communication is important for every human being, So when you get an oppurtunity to communicate so easily, and comfartabliy, you get addicted to it. Almost half the internet users, use internet for email services only. The big brands have recognised the potential. If you are wondering why Yahoo or Hotmail are still free, the reason behind it is that, these big brands go for targeted marketing, and they have made an name for themselves, So when it comes of trusting, you can trust them easily, Though I ma not saying that these mails are very good but yes they fullfill your daily need.
So when you come across and company offering Paid services the reason is that, the comoany wants an fixed customer, The offer you BIG MBs, much more speed, more storage, more reliablity, but then you see no major factors that will influnce your choice, You can easily get an 6mb mailbox from any reliable website, and then why would you store mails more that 6mb if you are an average user.
So my view is that, an average user should opt in for free mail services that paid, because of lack of major factors an this point.