Actually gmail was competing with HotMail/AOLMail and the biggest single thing that would get people to switch was 'better spam control.'
All you need to do is to tell a bunch of really smart engineers, "Here is this hugely important problem to solve, you probably aren't smart enough to solve it but we'll listen to what you have to say." And you get every engineer spending their 20% time burning first through the 'easy' fixes which don't actually work and then on to more 'interesting' fixes that kinda do, and finally some real puzzle masters doing things you would not expect but actually nail a lot of spam. And after you've done that then you have a number of people who really get a kick out of this sort of intellectual battle of wits, and you pull them together and make them the 'spam team'. Voila' achievement unlocked.
I still remember being blown away when I switched. I'd given up on SPAM. My wife still uses Yahoo and sometimes I'll go into her email to help with something and be shocked by how much she gets. Spam control is also the reason my two daughters have Gmail accounts so Google is capturing the next generation. (On a random side note my kids were actually disappointed when Buzz went away. They were all using it as their first SN experience as they were too young to be allowed access to anything else)
All you need to do is to tell a bunch of really smart engineers, "Here is this hugely important problem to solve, you probably aren't smart enough to solve it but we'll listen to what you have to say." And you get every engineer spending their 20% time burning first through the 'easy' fixes which don't actually work and then on to more 'interesting' fixes that kinda do, and finally some real puzzle masters doing things you would not expect but actually nail a lot of spam. And after you've done that then you have a number of people who really get a kick out of this sort of intellectual battle of wits, and you pull them together and make them the 'spam team'. Voila' achievement unlocked.